diff --git a/extensions/elasticsearch/ActiveRecord.php b/extensions/elasticsearch/ActiveRecord.php
index b04e67d..d6ada20 100644
--- a/extensions/elasticsearch/ActiveRecord.php
+++ b/extensions/elasticsearch/ActiveRecord.php
@@ -10,6 +10,8 @@ namespace yii\elasticsearch;
 use yii\base\InvalidCallException;
 use yii\base\InvalidConfigException;
 use yii\base\NotSupportedException;
+use yii\db\ActiveRecordInterface;
+use yii\db\BaseActiveRecord;
 use yii\helpers\Inflector;
 use yii\helpers\Json;
 use yii\helpers\StringHelper;
@@ -42,7 +44,7 @@ use yii\helpers\StringHelper;
  * @author Carsten Brandt <mail@cebe.cc>
  * @since 2.0
  */
-class ActiveRecord extends \yii\db\ActiveRecord
+class ActiveRecord extends BaseActiveRecord
 {
 	const PRIMARY_KEY_NAME = 'id';
 
@@ -428,47 +430,4 @@ class ActiveRecord extends \yii\db\ActiveRecord
 		}
 		return $n;
 	}
-
-	/**
-	 * @inheritdoc
-	 */
-	public static function updateAllCounters($counters, $condition = null, $params = [])
-	{
-		throw new NotSupportedException('Update Counters is not supported by elasticsearch ActiveRecord.');
-	}
-
-	/**
-	 * @inheritdoc
-	 */
-	public static function getTableSchema()
-	{
-		throw new NotSupportedException('getTableSchema() is not supported by elasticsearch ActiveRecord.');
-	}
-
-	/**
-	 * @inheritdoc
-	 */
-	public static function tableName()
-	{
-		return static::index() . '/' . static::type();
-	}
-
-	/**
-	 * @inheritdoc
-	 */
-	public static function findBySql($sql, $params = [])
-	{
-		throw new NotSupportedException('findBySql() is not supported by elasticsearch ActiveRecord.');
-	}
-
-	/**
-	 * Returns a value indicating whether the specified operation is transactional in the current [[scenario]].
-	 * This method will always return false as transactional operations are not supported by elasticsearch.
-	 * @param integer $operation the operation to check. Possible values are [[OP_INSERT]], [[OP_UPDATE]] and [[OP_DELETE]].
-	 * @return boolean whether the specified operation is transactional in the current [[scenario]].
-	 */
-	public function isTransactional($operation)
-	{
-		return false;
-	}
 }
diff --git a/extensions/redis/ActiveQuery.php b/extensions/redis/ActiveQuery.php
index 755fc6f..607b18e 100644
--- a/extensions/redis/ActiveQuery.php
+++ b/extensions/redis/ActiveQuery.php
@@ -132,7 +132,7 @@ class ActiveQuery extends \yii\base\Component implements ActiveQueryInterface
 			if ($db === null) {
 				$db = $modelClass::getDb();
 			}
-			return $db->executeCommand('LLEN', [$modelClass::tableName()]);
+			return $db->executeCommand('LLEN', [$modelClass::keyPrefix()]);
 		} else {
 			return $this->executeScript($db, 'Count');
 		}
@@ -296,7 +296,7 @@ class ActiveQuery extends \yii\base\Component implements ActiveQueryInterface
 		$data = [];
 		foreach($pks as $pk) {
 			if (++$i > $start && ($this->limit === null || $i <= $start + $this->limit)) {
-				$key = $modelClass::tableName() . ':a:' . $modelClass::buildKey($pk);
+				$key = $modelClass::keyPrefix() . ':a:' . $modelClass::buildKey($pk);
 				$result = $db->executeCommand('HGETALL', [$key]);
 				if (!empty($result)) {
 					$data[] = $result;
diff --git a/extensions/redis/ActiveRecord.php b/extensions/redis/ActiveRecord.php
index 1239a6c..f227ed1 100644
--- a/extensions/redis/ActiveRecord.php
+++ b/extensions/redis/ActiveRecord.php
@@ -9,6 +9,8 @@ namespace yii\redis;
 
 use yii\base\InvalidConfigException;
 use yii\base\NotSupportedException;
+use yii\db\BaseActiveRecord;
+use yii\helpers\Inflector;
 use yii\helpers\StringHelper;
 
 /**
@@ -34,7 +36,7 @@ use yii\helpers\StringHelper;
  * @author Carsten Brandt <mail@cebe.cc>
  * @since 2.0
  */
-class ActiveRecord extends \yii\db\ActiveRecord
+class ActiveRecord extends BaseActiveRecord
 {
 	/**
 	 * Returns the database connection used by this AR class.
@@ -87,6 +89,18 @@ class ActiveRecord extends \yii\db\ActiveRecord
 	}
 
 	/**
+	 * Declares prefix of the key that represents the keys that store this records in redis.
+	 * By default this method returns the class name as the table name by calling [[Inflector::camel2id()]].
+	 * For example, 'Customer' becomes 'customer', and 'OrderItem' becomes
+	 * 'order_item'. You may override this method if you want different key naming.
+	 * @return string the prefix to apply to all AR keys
+	 */
+	public static function keyPrefix()
+	{
+		return Inflector::camel2id(StringHelper::basename(get_called_class()), '_');
+	}
+
+	/**
 	 * @inheritdoc
 	 */
 	public function insert($runValidation = true, $attributes = null)
@@ -102,15 +116,15 @@ class ActiveRecord extends \yii\db\ActiveRecord
 			foreach ($this->primaryKey() as $key) {
 				$pk[$key] = $values[$key] = $this->getAttribute($key);
 				if ($pk[$key] === null) {
-					$pk[$key] = $values[$key] = $db->executeCommand('INCR', [static::tableName() . ':s:' . $key]);
+					$pk[$key] = $values[$key] = $db->executeCommand('INCR', [static::keyPrefix() . ':s:' . $key]);
 					$this->setAttribute($key, $values[$key]);
 				}
 			}
 //			}
 			// save pk in a findall pool
-			$db->executeCommand('RPUSH', [static::tableName(), static::buildKey($pk)]);
+			$db->executeCommand('RPUSH', [static::keyPrefix(), static::buildKey($pk)]);
 
-			$key = static::tableName() . ':a:' . static::buildKey($pk);
+			$key = static::keyPrefix() . ':a:' . static::buildKey($pk);
 			// save attributes
 			$args = [$key];
 			foreach($values as $attribute => $value) {
@@ -150,7 +164,7 @@ class ActiveRecord extends \yii\db\ActiveRecord
 		foreach(static::fetchPks($condition) as $pk) {
 			$newPk = $pk;
 			$pk = static::buildKey($pk);
-			$key = static::tableName() . ':a:' . $pk;
+			$key = static::keyPrefix() . ':a:' . $pk;
 			// save attributes
 			$args = [$key];
 			foreach($attributes as $attribute => $value) {
@@ -161,13 +175,13 @@ class ActiveRecord extends \yii\db\ActiveRecord
 				$args[] = $value;
 			}
 			$newPk = static::buildKey($newPk);
-			$newKey = static::tableName() . ':a:' . $newPk;
+			$newKey = static::keyPrefix() . ':a:' . $newPk;
 			// rename index if pk changed
 			if ($newPk != $pk) {
 				$db->executeCommand('MULTI');
 				$db->executeCommand('HMSET', $args);
-				$db->executeCommand('LINSERT', [static::tableName(), 'AFTER', $pk, $newPk]);
-				$db->executeCommand('LREM', [static::tableName(), 0, $pk]);
+				$db->executeCommand('LINSERT', [static::keyPrefix(), 'AFTER', $pk, $newPk]);
+				$db->executeCommand('LREM', [static::keyPrefix(), 0, $pk]);
 				$db->executeCommand('RENAME', [$key, $newKey]);
 				$db->executeCommand('EXEC');
 			} else {
@@ -201,7 +215,7 @@ class ActiveRecord extends \yii\db\ActiveRecord
 		$db = static::getDb();
 		$n=0;
 		foreach(static::fetchPks($condition) as $pk) {
-			$key = static::tableName() . ':a:' . static::buildKey($pk);
+			$key = static::keyPrefix() . ':a:' . static::buildKey($pk);
 			foreach($counters as $attribute => $value) {
 				$db->executeCommand('HINCRBY', [$key, $attribute, $value]);
 			}
@@ -233,8 +247,8 @@ class ActiveRecord extends \yii\db\ActiveRecord
 		$db->executeCommand('MULTI');
 		foreach($pks as $pk) {
 			$pk = static::buildKey($pk);
-			$db->executeCommand('LREM', [static::tableName(), 0, $pk]);
-			$attributeKeys[] = static::tableName() . ':a:' . $pk;
+			$db->executeCommand('LREM', [static::keyPrefix(), 0, $pk]);
+			$attributeKeys[] = static::keyPrefix() . ':a:' . $pk;
 		}
 		if (empty($attributeKeys)) {
 			$db->executeCommand('EXEC');
@@ -292,31 +306,4 @@ class ActiveRecord extends \yii\db\ActiveRecord
 		}
 		return md5(json_encode($key));
 	}
-
-	/**
-	 * @inheritdoc
-	 */
-	public static function getTableSchema()
-	{
-		throw new NotSupportedException('getTableSchema() is not supported by redis ActiveRecord.');
-	}
-
-	/**
-	 * @inheritdoc
-	 */
-	public static function findBySql($sql, $params = [])
-	{
-		throw new NotSupportedException('findBySql() is not supported by redis ActiveRecord.');
-	}
-
-	/**
-	 * Returns a value indicating whether the specified operation is transactional in the current [[scenario]].
-	 * This method will always return false as transactional operations are not supported by redis.
-	 * @param integer $operation the operation to check. Possible values are [[OP_INSERT]], [[OP_UPDATE]] and [[OP_DELETE]].
-	 * @return boolean whether the specified operation is transactional in the current [[scenario]].
-	 */
-	public function isTransactional($operation)
-	{
-		return false;
-	}
 }
diff --git a/extensions/redis/LuaScriptBuilder.php b/extensions/redis/LuaScriptBuilder.php
index 81dff3f..55bf455 100644
--- a/extensions/redis/LuaScriptBuilder.php
+++ b/extensions/redis/LuaScriptBuilder.php
@@ -29,7 +29,7 @@ class LuaScriptBuilder extends \yii\base\Object
 		// TODO add support for orderBy
 		/** @var ActiveRecord $modelClass */
 		$modelClass = $query->modelClass;
-		$key = $this->quoteValue($modelClass::tableName() . ':a:');
+		$key = $this->quoteValue($modelClass::keyPrefix() . ':a:');
 		return $this->build($query, "n=n+1 pks[n]=redis.call('HGETALL',$key .. pk)", 'pks');
 	}
 
@@ -43,7 +43,7 @@ class LuaScriptBuilder extends \yii\base\Object
 		// TODO add support for orderBy
 		/** @var ActiveRecord $modelClass */
 		$modelClass = $query->modelClass;
-		$key = $this->quoteValue($modelClass::tableName() . ':a:');
+		$key = $this->quoteValue($modelClass::keyPrefix() . ':a:');
 		return $this->build($query, "do return redis.call('HGETALL',$key .. pk) end", 'pks');
 	}
 
@@ -58,7 +58,7 @@ class LuaScriptBuilder extends \yii\base\Object
 		// TODO add support for orderBy and indexBy
 		/** @var ActiveRecord $modelClass */
 		$modelClass = $query->modelClass;
-		$key = $this->quoteValue($modelClass::tableName() . ':a:');
+		$key = $this->quoteValue($modelClass::keyPrefix() . ':a:');
 		return $this->build($query, "n=n+1 pks[n]=redis.call('HGET',$key .. pk," . $this->quoteValue($column) . ")", 'pks');
 	}
 
@@ -82,7 +82,7 @@ class LuaScriptBuilder extends \yii\base\Object
 	{
 		/** @var ActiveRecord $modelClass */
 		$modelClass = $query->modelClass;
-		$key = $this->quoteValue($modelClass::tableName() . ':a:');
+		$key = $this->quoteValue($modelClass::keyPrefix() . ':a:');
 		return $this->build($query, "n=n+redis.call('HGET',$key .. pk," . $this->quoteValue($column) . ")", 'n');
 	}
 
@@ -96,7 +96,7 @@ class LuaScriptBuilder extends \yii\base\Object
 	{
 		/** @var ActiveRecord $modelClass */
 		$modelClass = $query->modelClass;
-		$key = $this->quoteValue($modelClass::tableName() . ':a:');
+		$key = $this->quoteValue($modelClass::keyPrefix() . ':a:');
 		return $this->build($query, "n=n+1 if v==nil then v=0 end v=v+redis.call('HGET',$key .. pk," . $this->quoteValue($column) . ")", 'v/n');
 	}
 
@@ -110,7 +110,7 @@ class LuaScriptBuilder extends \yii\base\Object
 	{
 		/** @var ActiveRecord $modelClass */
 		$modelClass = $query->modelClass;
-		$key = $this->quoteValue($modelClass::tableName() . ':a:');
+		$key = $this->quoteValue($modelClass::keyPrefix() . ':a:');
 		return $this->build($query, "n=redis.call('HGET',$key .. pk," . $this->quoteValue($column) . ") if v==nil or n<v then v=n end", 'v');
 	}
 
@@ -124,7 +124,7 @@ class LuaScriptBuilder extends \yii\base\Object
 	{
 		/** @var ActiveRecord $modelClass */
 		$modelClass = $query->modelClass;
-		$key = $this->quoteValue($modelClass::tableName() . ':a:');
+		$key = $this->quoteValue($modelClass::keyPrefix() . ':a:');
 		return $this->build($query, "n=redis.call('HGET',$key .. pk," . $this->quoteValue($column) . ") if v==nil or n>v then v=n end", 'v');
 	}
 
@@ -152,7 +152,7 @@ class LuaScriptBuilder extends \yii\base\Object
 
 		/** @var ActiveRecord $modelClass */
 		$modelClass = $query->modelClass;
-		$key = $this->quoteValue($modelClass::tableName());
+		$key = $this->quoteValue($modelClass::keyPrefix());
 		$loadColumnValues = '';
 		foreach($columns as $column => $alias) {
 			$loadColumnValues .= "local $alias=redis.call('HGET',$key .. ':a:' .. pk, '$column')\n";
diff --git a/framework/yii/db/ActiveRecord.php b/framework/yii/db/ActiveRecord.php
index bb2016a..0d79d3e 100644
--- a/framework/yii/db/ActiveRecord.php
+++ b/framework/yii/db/ActiveRecord.php
@@ -39,45 +39,9 @@ use yii\helpers\Inflector;
  * @author Carsten Brandt <mail@cebe.cc>
  * @since 2.0
  */
-class ActiveRecord extends Model
+class ActiveRecord extends BaseActiveRecord
 {
 	/**
-	 * @event Event an event that is triggered when the record is initialized via [[init()]].
-	 */
-	const EVENT_INIT = 'init';
-	/**
-	 * @event Event an event that is triggered after the record is created and populated with query result.
-	 */
-	const EVENT_AFTER_FIND = 'afterFind';
-	/**
-	 * @event ModelEvent an event that is triggered before inserting a record.
-	 * You may set [[ModelEvent::isValid]] to be false to stop the insertion.
-	 */
-	const EVENT_BEFORE_INSERT = 'beforeInsert';
-	/**
-	 * @event Event an event that is triggered after a record is inserted.
-	 */
-	const EVENT_AFTER_INSERT = 'afterInsert';
-	/**
-	 * @event ModelEvent an event that is triggered before updating a record.
-	 * You may set [[ModelEvent::isValid]] to be false to stop the update.
-	 */
-	const EVENT_BEFORE_UPDATE = 'beforeUpdate';
-	/**
-	 * @event Event an event that is triggered after a record is updated.
-	 */
-	const EVENT_AFTER_UPDATE = 'afterUpdate';
-	/**
-	 * @event ModelEvent an event that is triggered before deleting a record.
-	 * You may set [[ModelEvent::isValid]] to be false to stop the deletion.
-	 */
-	const EVENT_BEFORE_DELETE = 'beforeDelete';
-	/**
-	 * @event Event an event that is triggered after a record is deleted.
-	 */
-	const EVENT_AFTER_DELETE = 'afterDelete';
-
-	/**
 	 * The insert operation. This is mainly used when overriding [[transactions()]] to specify which operations are transactional.
 	 */
 	const OP_INSERT = 0x01;
@@ -96,20 +60,6 @@ class ActiveRecord extends Model
 	const OP_ALL = 0x07;
 
 	/**
-	 * @var array attribute values indexed by attribute names
-	 */
-	private $_attributes = [];
-	/**
-	 * @var array old attribute values indexed by attribute names.
-	 */
-	private $_oldAttributes;
-	/**
-	 * @var array related models indexed by the relation names
-	 */
-	private $_related = [];
-
-
-	/**
 	 * Returns the database connection used by this AR class.
 	 * By default, the "db" application component is used as the database connection.
 	 * You may override this method if you want to use a different database connection.
@@ -121,41 +71,6 @@ class ActiveRecord extends Model
 	}
 
 	/**
-	 * Creates an [[ActiveQuery]] instance for query purpose.
-	 *
-	 * @include @yii/db/ActiveRecord-find.md
-	 *
-	 * @param mixed $q the query parameter. This can be one of the followings:
-	 *
-	 *  - a scalar value (integer or string): query by a single primary key value and return the
-	 *    corresponding record.
-	 *  - an array of name-value pairs: query by a set of column values and return a single record matching all of them.
-	 *  - null: return a new [[ActiveQuery]] object for further query purpose.
-	 *
-	 * @return ActiveQuery|ActiveRecord|null When `$q` is null, a new [[ActiveQuery]] instance
-	 * is returned; when `$q` is a scalar or an array, an ActiveRecord object matching it will be
-	 * returned (null will be returned if there is no matching).
-	 * @throws InvalidConfigException if the AR class does not have a primary key
-	 * @see createQuery()
-	 */
-	public static function find($q = null)
-	{
-		$query = static::createQuery();
-		if (is_array($q)) {
-			return $query->where($q)->one();
-		} elseif ($q !== null) {
-			// query by primary key
-			$primaryKey = static::primaryKey();
-			if (isset($primaryKey[0])) {
-				return $query->where([$primaryKey[0] => $q])->one();
-			} else {
-				throw new InvalidConfigException(get_called_class() . ' must have a primary key.');
-			}
-		}
-		return $query;
-	}
-
-	/**
 	 * Creates an [[ActiveQuery]] instance with a given SQL statement.
 	 *
 	 * Note that because the SQL statement is already specified, calling additional
@@ -309,31 +224,13 @@ class ActiveRecord extends Model
 	}
 
 	/**
-	 * Returns the name of the column that stores the lock version for implementing optimistic locking.
-	 *
-	 * Optimistic locking allows multiple users to access the same record for edits and avoids
-	 * potential conflicts. In case when a user attempts to save the record upon some staled data
-	 * (because another user has modified the data), a [[StaleObjectException]] exception will be thrown,
-	 * and the update or deletion is skipped.
-	 *
-	 * Optimistic locking is only supported by [[update()]] and [[delete()]].
-	 *
-	 * To use Optimistic locking:
-	 *
-	 * 1. Create a column to store the version number of each row. The column type should be `BIGINT DEFAULT 0`.
-	 *    Override this method to return the name of this column.
-	 * 2. In the Web form that collects the user input, add a hidden field that stores
-	 *    the lock version of the recording being updated.
-	 * 3. In the controller action that does the data updating, try to catch the [[StaleObjectException]]
-	 *    and implement necessary business logic (e.g. merging the changes, prompting stated data)
-	 *    to resolve the conflict.
-	 *
-	 * @return string the column name that stores the lock version of a table row.
-	 * If null is returned (default implemented), optimistic locking will not be supported.
+	 * Returns the list of all attribute names of the model.
+	 * The default implementation will return all column names of the table associated with this AR class.
+	 * @return array list of attribute names.
 	 */
-	public function optimisticLock()
+	public function attributes()
 	{
-		return null;
+		return array_keys(static::getTableSchema()->columns);
 	}
 
 	/**
@@ -369,161 +266,6 @@ class ActiveRecord extends Model
 	}
 
 	/**
-	 * PHP getter magic method.
-	 * This method is overridden so that attributes and related objects can be accessed like properties.
-	 * @param string $name property name
-	 * @return mixed property value
-	 * @see getAttribute()
-	 */
-	public function __get($name)
-	{
-		if (isset($this->_attributes[$name]) || array_key_exists($name, $this->_attributes)) {
-			return $this->_attributes[$name];
-		} elseif ($this->hasAttribute($name)) {
-			return null;
-		} else {
-			if (isset($this->_related[$name]) || array_key_exists($name, $this->_related)) {
-				return $this->_related[$name];
-			}
-			$value = parent::__get($name);
-			if ($value instanceof ActiveRelationInterface) {
-				return $this->_related[$name] = $value->multiple ? $value->all() : $value->one();
-			} else {
-				return $value;
-			}
-		}
-	}
-
-	/**
-	 * PHP setter magic method.
-	 * This method is overridden so that AR attributes can be accessed like properties.
-	 * @param string $name property name
-	 * @param mixed $value property value
-	 */
-	public function __set($name, $value)
-	{
-		if ($this->hasAttribute($name)) {
-			$this->_attributes[$name] = $value;
-		} else {
-			parent::__set($name, $value);
-		}
-	}
-
-	/**
-	 * Checks if a property value is null.
-	 * This method overrides the parent implementation by checking if the named attribute is null or not.
-	 * @param string $name the property name or the event name
-	 * @return boolean whether the property value is null
-	 */
-	public function __isset($name)
-	{
-		try {
-			return $this->__get($name) !== null;
-		} catch (\Exception $e) {
-			return false;
-		}
-	}
-
-	/**
-	 * Sets a component property to be null.
-	 * This method overrides the parent implementation by clearing
-	 * the specified attribute value.
-	 * @param string $name the property name or the event name
-	 */
-	public function __unset($name)
-	{
-		if ($this->hasAttribute($name)) {
-			unset($this->_attributes[$name]);
-		} else {
-			if (isset($this->_related[$name])) {
-				unset($this->_related[$name]);
-			} else {
-				parent::__unset($name);
-			}
-		}
-	}
-
-	/**
-	 * Declares a `has-one` relation.
-	 * The declaration is returned in terms of an [[ActiveRelation]] instance
-	 * through which the related record can be queried and retrieved back.
-	 *
-	 * A `has-one` relation means that there is at most one related record matching
-	 * the criteria set by this relation, e.g., a customer has one country.
-	 *
-	 * For example, to declare the `country` relation for `Customer` class, we can write
-	 * the following code in the `Customer` class:
-	 *
-	 * ~~~
-	 * public function getCountry()
-	 * {
-	 *     return $this->hasOne(Country::className(), ['id' => 'country_id']);
-	 * }
-	 * ~~~
-	 *
-	 * Note that in the above, the 'id' key in the `$link` parameter refers to an attribute name
-	 * in the related class `Country`, while the 'country_id' value refers to an attribute name
-	 * in the current AR class.
-	 *
-	 * Call methods declared in [[ActiveRelation]] to further customize the relation.
-	 *
-	 * @param string $class the class name of the related record
-	 * @param array $link the primary-foreign key constraint. The keys of the array refer to
-	 * the attributes of the record associated with the `$class` model, while the values of the
-	 * array refer to the corresponding attributes in **this** AR class.
-	 * @return ActiveRelationInterface the relation object.
-	 */
-	public function hasOne($class, $link)
-	{
-		/** @var ActiveRecord $class */
-		return $class::createActiveRelation([
-			'modelClass' => $class,
-			'primaryModel' => $this,
-			'link' => $link,
-			'multiple' => false,
-		]);
-	}
-
-	/**
-	 * Declares a `has-many` relation.
-	 * The declaration is returned in terms of an [[ActiveRelation]] instance
-	 * through which the related record can be queried and retrieved back.
-	 *
-	 * A `has-many` relation means that there are multiple related records matching
-	 * the criteria set by this relation, e.g., a customer has many orders.
-	 *
-	 * For example, to declare the `orders` relation for `Customer` class, we can write
-	 * the following code in the `Customer` class:
-	 *
-	 * ~~~
-	 * public function getOrders()
-	 * {
-	 *     return $this->hasMany(Order::className(), ['customer_id' => 'id']);
-	 * }
-	 * ~~~
-	 *
-	 * Note that in the above, the 'customer_id' key in the `$link` parameter refers to
-	 * an attribute name in the related class `Order`, while the 'id' value refers to
-	 * an attribute name in the current AR class.
-	 *
-	 * @param string $class the class name of the related record
-	 * @param array $link the primary-foreign key constraint. The keys of the array refer to
-	 * the attributes of the record associated with the `$class` model, while the values of the
-	 * array refer to the corresponding attributes in **this** AR class.
-	 * @return ActiveRelationInterface the relation object.
-	 */
-	public function hasMany($class, $link)
-	{
-		/** @var ActiveRecord $class */
-		return $class::createActiveRelation([
-			'modelClass' => $class,
-			'primaryModel' => $this,
-			'link' => $link,
-			'multiple' => true,
-		]);
-	}
-
-	/**
 	 * Creates an [[ActiveRelation]] instance.
 	 * This method is called by [[hasOne()]] and [[hasMany()]] to create a relation instance.
 	 * You may override this method to return a customized relation.
@@ -536,208 +278,6 @@ class ActiveRecord extends Model
 	}
 
 	/**
-	 * Populates the named relation with the related records.
-	 * Note that this method does not check if the relation exists or not.
-	 * @param string $name the relation name (case-sensitive)
-	 * @param ActiveRecord|array|null the related records to be populated into the relation.
-	 */
-	public function populateRelation($name, $records)
-	{
-		$this->_related[$name] = $records;
-	}
-
-	/**
-	 * Check whether the named relation has been populated with records.
-	 * @param string $name the relation name (case-sensitive)
-	 * @return bool whether relation has been populated with records.
-	 */
-	public function isRelationPopulated($name)
-	{
-		return array_key_exists($name, $this->_related);
-	}
-
-	/**
-	 * Returns all populated relations.
-	 * @return array an array of relation data indexed by relation names.
-	 */
-	public function getPopulatedRelations()
-	{
-		return $this->_related;
-	}
-
-	/**
-	 * Returns the list of all attribute names of the model.
-	 * The default implementation will return all column names of the table associated with this AR class.
-	 * @return array list of attribute names.
-	 */
-	public function attributes()
-	{
-		return array_keys(static::getTableSchema()->columns);
-	}
-
-	/**
-	 * Returns a value indicating whether the model has an attribute with the specified name.
-	 * @param string $name the name of the attribute
-	 * @return boolean whether the model has an attribute with the specified name.
-	 */
-	public function hasAttribute($name)
-	{
-		return isset($this->_attributes[$name]) || in_array($name, $this->attributes());
-	}
-
-	/**
-	 * Returns the named attribute value.
-	 * If this record is the result of a query and the attribute is not loaded,
-	 * null will be returned.
-	 * @param string $name the attribute name
-	 * @return mixed the attribute value. Null if the attribute is not set or does not exist.
-	 * @see hasAttribute()
-	 */
-	public function getAttribute($name)
-	{
-		return isset($this->_attributes[$name]) ? $this->_attributes[$name] : null;
-	}
-
-	/**
-	 * Sets the named attribute value.
-	 * @param string $name the attribute name
-	 * @param mixed $value the attribute value.
-	 * @throws InvalidParamException if the named attribute does not exist.
-	 * @see hasAttribute()
-	 */
-	public function setAttribute($name, $value)
-	{
-		if ($this->hasAttribute($name)) {
-			$this->_attributes[$name] = $value;
-		} else {
-			throw new InvalidParamException(get_class($this) . ' has no attribute named "' . $name . '".');
-		}
-	}
-
-	/**
-	 * Returns the old attribute values.
-	 * @return array the old attribute values (name-value pairs)
-	 */
-	public function getOldAttributes()
-	{
-		return $this->_oldAttributes === null ? [] : $this->_oldAttributes;
-	}
-
-	/**
-	 * Sets the old attribute values.
-	 * All existing old attribute values will be discarded.
-	 * @param array $values old attribute values to be set.
-	 */
-	public function setOldAttributes($values)
-	{
-		$this->_oldAttributes = $values;
-	}
-
-	/**
-	 * Returns the old value of the named attribute.
-	 * If this record is the result of a query and the attribute is not loaded,
-	 * null will be returned.
-	 * @param string $name the attribute name
-	 * @return mixed the old attribute value. Null if the attribute is not loaded before
-	 * or does not exist.
-	 * @see hasAttribute()
-	 */
-	public function getOldAttribute($name)
-	{
-		return isset($this->_oldAttributes[$name]) ? $this->_oldAttributes[$name] : null;
-	}
-
-	/**
-	 * Sets the old value of the named attribute.
-	 * @param string $name the attribute name
-	 * @param mixed $value the old attribute value.
-	 * @throws InvalidParamException if the named attribute does not exist.
-	 * @see hasAttribute()
-	 */
-	public function setOldAttribute($name, $value)
-	{
-		if (isset($this->_oldAttributes[$name]) || $this->hasAttribute($name)) {
-			$this->_oldAttributes[$name] = $value;
-		} else {
-			throw new InvalidParamException(get_class($this) . ' has no attribute named "' . $name . '".');
-		}
-	}
-
-	/**
-	 * Returns a value indicating whether the named attribute has been changed.
-	 * @param string $name the name of the attribute
-	 * @return boolean whether the attribute has been changed
-	 */
-	public function isAttributeChanged($name)
-	{
-		if (isset($this->_attributes[$name], $this->_oldAttributes[$name])) {
-			return $this->_attributes[$name] !== $this->_oldAttributes[$name];
-		} else {
-			return isset($this->_attributes[$name]) || isset($this->_oldAttributes[$name]);
-		}
-	}
-
-	/**
-	 * Returns the attribute values that have been modified since they are loaded or saved most recently.
-	 * @param string[]|null $names the names of the attributes whose values may be returned if they are
-	 * changed recently. If null, [[attributes()]] will be used.
-	 * @return array the changed attribute values (name-value pairs)
-	 */
-	public function getDirtyAttributes($names = null)
-	{
-		if ($names === null) {
-			$names = $this->attributes();
-		}
-		$names = array_flip($names);
-		$attributes = [];
-		if ($this->_oldAttributes === null) {
-			foreach ($this->_attributes as $name => $value) {
-				if (isset($names[$name])) {
-					$attributes[$name] = $value;
-				}
-			}
-		} else {
-			foreach ($this->_attributes as $name => $value) {
-				if (isset($names[$name]) && (!array_key_exists($name, $this->_oldAttributes) || $value !== $this->_oldAttributes[$name])) {
-					$attributes[$name] = $value;
-				}
-			}
-		}
-		return $attributes;
-	}
-
-	/**
-	 * Saves the current record.
-	 *
-	 * This method will call [[insert()]] when [[isNewRecord]] is true, or [[update()]]
-	 * when [[isNewRecord]] is false.
-	 *
-	 * For example, to save a customer record:
-	 *
-	 * ~~~
-	 * $customer = new Customer;  // or $customer = Customer::find($id);
-	 * $customer->name = $name;
-	 * $customer->email = $email;
-	 * $customer->save();
-	 * ~~~
-	 *
-	 *
-	 * @param boolean $runValidation whether to perform validation before saving the record.
-	 * If the validation fails, the record will not be saved to database.
-	 * @param array $attributes list of attributes that need to be saved. Defaults to null,
-	 * meaning all attributes that are loaded from DB will be saved.
-	 * @return boolean whether the saving succeeds
-	 */
-	public function save($runValidation = true, $attributes = null)
-	{
-		if ($this->getIsNewRecord()) {
-			return $this->insert($runValidation, $attributes);
-		} else {
-			return $this->update($runValidation, $attributes) !== false;
-		}
-	}
-
-	/**
 	 * Inserts a row into the associated database table using the attribute values of this record.
 	 *
 	 * This method performs the following steps in order:
@@ -810,8 +350,8 @@ class ActiveRecord extends Model
 		}
 		$values = $this->getDirtyAttributes($attributes);
 		if (empty($values)) {
-			foreach ($this->primaryKey() as $key) {
-				$values[$key] = isset($this->_attributes[$key]) ? $this->_attributes[$key] : null;
+			foreach ($this->getPrimaryKey(true) as $key => $value) {
+				$values[$key] = $value;
 			}
 		}
 		$db = static::getDb();
@@ -822,14 +362,16 @@ class ActiveRecord extends Model
 		$table = $this->getTableSchema();
 		if ($table->sequenceName !== null) {
 			foreach ($table->primaryKey as $name) {
-				if (!isset($this->_attributes[$name])) {
-					$this->_oldAttributes[$name] = $this->_attributes[$name] = $db->getLastInsertID($table->sequenceName);
+				if ($this->getAttribute($name) === null) {
+					$id = $db->getLastInsertID($table->sequenceName);
+					$this->setAttribute($name, $id);
+					$this->setOldAttribute($name, $id);
 					break;
 				}
 			}
 		}
 		foreach ($values as $name => $value) {
-			$this->_oldAttributes[$name] = $value;
+			$this->setOldAttribute($name, $value);
 		}
 		$this->afterSave(true);
 		return true;
@@ -911,73 +453,6 @@ class ActiveRecord extends Model
 	}
 
 	/**
-	 * @see CActiveRecord::update()
-	 * @throws StaleObjectException
-	 */
-	private function updateInternal($attributes = null)
-	{
-		if (!$this->beforeSave(false)) {
-			return false;
-		}
-		$values = $this->getDirtyAttributes($attributes);
-		if (empty($values)) {
-			$this->afterSave(false);
-			return 0;
-		}
-		$condition = $this->getOldPrimaryKey(true);
-		$lock = $this->optimisticLock();
-		if ($lock !== null) {
-			if (!isset($values[$lock])) {
-				$values[$lock] = $this->$lock + 1;
-			}
-			$condition[$lock] = $this->$lock;
-		}
-		// We do not check the return value of updateAll() because it's possible
-		// that the UPDATE statement doesn't change anything and thus returns 0.
-		$rows = $this->updateAll($values, $condition);
-
-		if ($lock !== null && !$rows) {
-			throw new StaleObjectException('The object being updated is outdated.');
-		}
-
-		foreach ($values as $name => $value) {
-			$this->_oldAttributes[$name] = $this->_attributes[$name];
-		}
-		$this->afterSave(false);
-		return $rows;
-	}
-
-	/**
-	 * Updates one or several counter columns for the current AR object.
-	 * Note that this method differs from [[updateAllCounters()]] in that it only
-	 * saves counters for the current AR object.
-	 *
-	 * An example usage is as follows:
-	 *
-	 * ~~~
-	 * $post = Post::find($id);
-	 * $post->updateCounters(['view_count' => 1]);
-	 * ~~~
-	 *
-	 * @param array $counters the counters to be updated (attribute name => increment value)
-	 * Use negative values if you want to decrement the counters.
-	 * @return boolean whether the saving is successful
-	 * @see updateAllCounters()
-	 */
-	public function updateCounters($counters)
-	{
-		if ($this->updateAllCounters($counters, $this->getOldPrimaryKey(true)) > 0) {
-			foreach ($counters as $name => $value) {
-				$this->_attributes[$name] += $value;
-				$this->_oldAttributes[$name] = $this->_attributes[$name];
-			}
-			return true;
-		} else {
-			return false;
-		}
-	}
-
-	/**
 	 * Deletes the table row corresponding to this active record.
 	 *
 	 * This method performs the following steps in order:
@@ -1014,7 +489,7 @@ class ActiveRecord extends Model
 				if ($lock !== null && !$result) {
 					throw new StaleObjectException('The object being deleted is outdated.');
 				}
-				$this->_oldAttributes = null;
+				$this->setOldAttributes(null);
 				$this->afterDelete();
 			}
 			if ($transaction !== null) {
@@ -1034,149 +509,6 @@ class ActiveRecord extends Model
 	}
 
 	/**
-	 * Returns a value indicating whether the current record is new.
-	 * @return boolean whether the record is new and should be inserted when calling [[save()]].
-	 */
-	public function getIsNewRecord()
-	{
-		return $this->_oldAttributes === null;
-	}
-
-	/**
-	 * Sets the value indicating whether the record is new.
-	 * @param boolean $value whether the record is new and should be inserted when calling [[save()]].
-	 * @see getIsNewRecord()
-	 */
-	public function setIsNewRecord($value)
-	{
-		$this->_oldAttributes = $value ? null : $this->_attributes;
-	}
-
-	/**
-	 * Initializes the object.
-	 * This method is called at the end of the constructor.
-	 * The default implementation will trigger an [[EVENT_INIT]] event.
-	 * If you override this method, make sure you call the parent implementation at the end
-	 * to ensure triggering of the event.
-	 */
-	public function init()
-	{
-		parent::init();
-		$this->trigger(self::EVENT_INIT);
-	}
-
-	/**
-	 * This method is called when the AR object is created and populated with the query result.
-	 * The default implementation will trigger an [[EVENT_AFTER_FIND]] event.
-	 * When overriding this method, make sure you call the parent implementation to ensure the
-	 * event is triggered.
-	 */
-	public function afterFind()
-	{
-		$this->trigger(self::EVENT_AFTER_FIND);
-	}
-
-	/**
-	 * This method is called at the beginning of inserting or updating a record.
-	 * The default implementation will trigger an [[EVENT_BEFORE_INSERT]] event when `$insert` is true,
-	 * or an [[EVENT_BEFORE_UPDATE]] event if `$insert` is false.
-	 * When overriding this method, make sure you call the parent implementation like the following:
-	 *
-	 * ~~~
-	 * public function beforeSave($insert)
-	 * {
-	 *     if (parent::beforeSave($insert)) {
-	 *         // ...custom code here...
-	 *         return true;
-	 *     } else {
-	 *         return false;
-	 *     }
-	 * }
-	 * ~~~
-	 *
-	 * @param boolean $insert whether this method called while inserting a record.
-	 * If false, it means the method is called while updating a record.
-	 * @return boolean whether the insertion or updating should continue.
-	 * If false, the insertion or updating will be cancelled.
-	 */
-	public function beforeSave($insert)
-	{
-		$event = new ModelEvent;
-		$this->trigger($insert ? self::EVENT_BEFORE_INSERT : self::EVENT_BEFORE_UPDATE, $event);
-		return $event->isValid;
-	}
-
-	/**
-	 * This method is called at the end of inserting or updating a record.
-	 * The default implementation will trigger an [[EVENT_AFTER_INSERT]] event when `$insert` is true,
-	 * or an [[EVENT_AFTER_UPDATE]] event if `$insert` is false.
-	 * When overriding this method, make sure you call the parent implementation so that
-	 * the event is triggered.
-	 * @param boolean $insert whether this method called while inserting a record.
-	 * If false, it means the method is called while updating a record.
-	 */
-	public function afterSave($insert)
-	{
-		$this->trigger($insert ? self::EVENT_AFTER_INSERT : self::EVENT_AFTER_UPDATE);
-	}
-
-	/**
-	 * This method is invoked before deleting a record.
-	 * The default implementation raises the [[EVENT_BEFORE_DELETE]] event.
-	 * When overriding this method, make sure you call the parent implementation like the following:
-	 *
-	 * ~~~
-	 * public function beforeDelete()
-	 * {
-	 *     if (parent::beforeDelete()) {
-	 *         // ...custom code here...
-	 *         return true;
-	 *     } else {
-	 *         return false;
-	 *     }
-	 * }
-	 * ~~~
-	 *
-	 * @return boolean whether the record should be deleted. Defaults to true.
-	 */
-	public function beforeDelete()
-	{
-		$event = new ModelEvent;
-		$this->trigger(self::EVENT_BEFORE_DELETE, $event);
-		return $event->isValid;
-	}
-
-	/**
-	 * This method is invoked after deleting a record.
-	 * The default implementation raises the [[EVENT_AFTER_DELETE]] event.
-	 * You may override this method to do postprocessing after the record is deleted.
-	 * Make sure you call the parent implementation so that the event is raised properly.
-	 */
-	public function afterDelete()
-	{
-		$this->trigger(self::EVENT_AFTER_DELETE);
-	}
-
-	/**
-	 * Repopulates this active record with the latest data.
-	 * @return boolean whether the row still exists in the database. If true, the latest data
-	 * will be populated to this active record. Otherwise, this record will remain unchanged.
-	 */
-	public function refresh()
-	{
-		$record = $this->find($this->getPrimaryKey(true));
-		if ($record === null) {
-			return false;
-		}
-		foreach ($this->attributes() as $name) {
-			$this->_attributes[$name] = isset($record->_attributes[$name]) ? $record->_attributes[$name] : null;
-		}
-		$this->_oldAttributes = $this->_attributes;
-		$this->_related = [];
-		return true;
-	}
-
-	/**
 	 * Returns a value indicating whether the given active record is the same as the current one.
 	 * The comparison is made by comparing the table names and the primary key values of the two active records.
 	 * If one of the records [[isNewRecord|is new]] they are also considered not equal.
@@ -1192,348 +524,6 @@ class ActiveRecord extends Model
 	}
 
 	/**
-	 * Returns the primary key value(s).
-	 * @param boolean $asArray whether to return the primary key value as an array. If true,
-	 * the return value will be an array with column names as keys and column values as values.
-	 * Note that for composite primary keys, an array will always be returned regardless of this parameter value.
-	 * @property mixed The primary key value. An array (column name => column value) is returned if
-	 * the primary key is composite. A string is returned otherwise (null will be returned if
-	 * the key value is null).
-	 * @return mixed the primary key value. An array (column name => column value) is returned if the primary key
-	 * is composite or `$asArray` is true. A string is returned otherwise (null will be returned if
-	 * the key value is null).
-	 */
-	public function getPrimaryKey($asArray = false)
-	{
-		$keys = $this->primaryKey();
-		if (count($keys) === 1 && !$asArray) {
-			return isset($this->_attributes[$keys[0]]) ? $this->_attributes[$keys[0]] : null;
-		} else {
-			$values = [];
-			foreach ($keys as $name) {
-				$values[$name] = isset($this->_attributes[$name]) ? $this->_attributes[$name] : null;
-			}
-			return $values;
-		}
-	}
-
-	/**
-	 * Returns the old primary key value(s).
-	 * This refers to the primary key value that is populated into the record
-	 * after executing a find method (e.g. find(), findAll()).
-	 * The value remains unchanged even if the primary key attribute is manually assigned with a different value.
-	 * @param boolean $asArray whether to return the primary key value as an array. If true,
-	 * the return value will be an array with column name as key and column value as value.
-	 * If this is false (default), a scalar value will be returned for non-composite primary key.
-	 * @property mixed The old primary key value. An array (column name => column value) is
-	 * returned if the primary key is composite. A string is returned otherwise (null will be
-	 * returned if the key value is null).
-	 * @return mixed the old primary key value. An array (column name => column value) is returned if the primary key
-	 * is composite or `$asArray` is true. A string is returned otherwise (null will be returned if
-	 * the key value is null).
-	 */
-	public function getOldPrimaryKey($asArray = false)
-	{
-		$keys = $this->primaryKey();
-		if (count($keys) === 1 && !$asArray) {
-			return isset($this->_oldAttributes[$keys[0]]) ? $this->_oldAttributes[$keys[0]] : null;
-		} else {
-			$values = [];
-			foreach ($keys as $name) {
-				$values[$name] = isset($this->_oldAttributes[$name]) ? $this->_oldAttributes[$name] : null;
-			}
-			return $values;
-		}
-	}
-
-	/**
-	 * Creates an active record object using a row of data.
-	 * This method is called by [[ActiveQuery]] to populate the query results
-	 * into Active Records. It is not meant to be used to create new records.
-	 * @param array $row attribute values (name => value)
-	 * @return ActiveRecord the newly created active record.
-	 */
-	public static function create($row)
-	{
-		$record = static::instantiate($row);
-		$columns = array_flip($record->attributes());
-		foreach ($row as $name => $value) {
-			if (isset($columns[$name])) {
-				$record->_attributes[$name] = $value;
-			} else {
-				$record->$name = $value;
-			}
-		}
-		$record->_oldAttributes = $record->_attributes;
-		$record->afterFind();
-		return $record;
-	}
-
-	/**
-	 * Creates an active record instance.
-	 * This method is called by [[create()]].
-	 * You may override this method if the instance being created
-	 * depends on the row data to be populated into the record.
-	 * For example, by creating a record based on the value of a column,
-	 * you may implement the so-called single-table inheritance mapping.
-	 * @param array $row row data to be populated into the record.
-	 * @return ActiveRecord the newly created active record
-	 */
-	public static function instantiate($row)
-	{
-		return new static;
-	}
-
-	/**
-	 * Returns whether there is an element at the specified offset.
-	 * This method is required by the interface ArrayAccess.
-	 * @param mixed $offset the offset to check on
-	 * @return boolean whether there is an element at the specified offset.
-	 */
-	public function offsetExists($offset)
-	{
-		return $this->__isset($offset);
-	}
-
-	/**
-	 * Returns the relation object with the specified name.
-	 * A relation is defined by a getter method which returns an [[ActiveRelation]] object.
-	 * It can be declared in either the Active Record class itself or one of its behaviors.
-	 * @param string $name the relation name
-	 * @return ActiveRelation the relation object
-	 * @throws InvalidParamException if the named relation does not exist.
-	 */
-	public function getRelation($name)
-	{
-		$getter = 'get' . $name;
-		try {
-			$relation = $this->$getter();
-			if ($relation instanceof ActiveRelationInterface) {
-				return $relation;
-			} else {
-				throw new InvalidParamException(get_class($this) . ' has no relation named "' . $name . '".');
-			}
-		} catch (UnknownMethodException $e) {
-			throw new InvalidParamException(get_class($this) . ' has no relation named "' . $name . '".', 0, $e);
-		}
-	}
-
-	/**
-	 * Establishes the relationship between two models.
-	 *
-	 * The relationship is established by setting the foreign key value(s) in one model
-	 * to be the corresponding primary key value(s) in the other model.
-	 * The model with the foreign key will be saved into database without performing validation.
-	 *
-	 * If the relationship involves a pivot table, a new row will be inserted into the
-	 * pivot table which contains the primary key values from both models.
-	 *
-	 * Note that this method requires that the primary key value is not null.
-	 *
-	 * @param string $name the case sensitive name of the relationship
-	 * @param ActiveRecord $model the model to be linked with the current one.
-	 * @param array $extraColumns additional column values to be saved into the pivot table.
-	 * This parameter is only meaningful for a relationship involving a pivot table
-	 * (i.e., a relation set with `[[ActiveRelation::via()]]` or `[[ActiveRelation::viaTable()]]`.)
-	 * @throws InvalidCallException if the method is unable to link two models.
-	 */
-	public function link($name, $model, $extraColumns = [])
-	{
-		$relation = $this->getRelation($name);
-
-		if ($relation->via !== null) {
-			if ($this->getIsNewRecord() || $model->getIsNewRecord()) {
-				throw new InvalidCallException('Unable to link models: both models must NOT be newly created.');
-			}
-			if (is_array($relation->via)) {
-				/** @var ActiveRelation $viaRelation */
-				list($viaName, $viaRelation) = $relation->via;
-				$viaClass = $viaRelation->modelClass;
-				// unset $viaName so that it can be reloaded to reflect the change
-				unset($this->_related[$viaName]);
-			} else {
-				$viaRelation = $relation->via;
-				$viaTable = reset($relation->via->from);
-			}
-			$columns = [];
-			foreach ($viaRelation->link as $a => $b) {
-				$columns[$a] = $this->$b;
-			}
-			foreach ($relation->link as $a => $b) {
-				$columns[$b] = $model->$a;
-			}
-			foreach ($extraColumns as $k => $v) {
-				$columns[$k] = $v;
-			}
-			if (is_array($relation->via)) {
-				/** @var $viaClass ActiveRecord */
-				/** @var $record ActiveRecord */
-				$record = new $viaClass();
-				foreach($columns as $column => $value) {
-					$record->$column = $value;
-				}
-				$record->insert(false);
-			} else {
-				/** @var $viaTable string */
-				static::getDb()->createCommand()
-					->insert($viaTable, $columns)->execute();
-			}
-		} else {
-			$p1 = $model->isPrimaryKey(array_keys($relation->link));
-			$p2 = $this->isPrimaryKey(array_values($relation->link));
-			if ($p1 && $p2) {
-				if ($this->getIsNewRecord() && $model->getIsNewRecord()) {
-					throw new InvalidCallException('Unable to link models: both models are newly created.');
-				} elseif ($this->getIsNewRecord()) {
-					$this->bindModels(array_flip($relation->link), $this, $model);
-				} else {
-					$this->bindModels($relation->link, $model, $this);
-				}
-			} elseif ($p1) {
-				$this->bindModels(array_flip($relation->link), $this, $model);
-			} elseif ($p2) {
-				$this->bindModels($relation->link, $model, $this);
-			} else {
-				throw new InvalidCallException('Unable to link models: the link does not involve any primary key.');
-			}
-		}
-
-		// update lazily loaded related objects
-		if (!$relation->multiple) {
-			$this->_related[$name] = $model;
-		} elseif (isset($this->_related[$name])) {
-			if ($relation->indexBy !== null) {
-				$indexBy = $relation->indexBy;
-				$this->_related[$name][$model->$indexBy] = $model;
-			} else {
-				$this->_related[$name][] = $model;
-			}
-		}
-	}
-
-	/**
-	 * Destroys the relationship between two models.
-	 *
-	 * The model with the foreign key of the relationship will be deleted if `$delete` is true.
-	 * Otherwise, the foreign key will be set null and the model will be saved without validation.
-	 *
-	 * @param string $name the case sensitive name of the relationship.
-	 * @param ActiveRecord $model the model to be unlinked from the current one.
-	 * @param boolean $delete whether to delete the model that contains the foreign key.
-	 * If false, the model's foreign key will be set null and saved.
-	 * If true, the model containing the foreign key will be deleted.
-	 * @throws InvalidCallException if the models cannot be unlinked
-	 */
-	public function unlink($name, $model, $delete = false)
-	{
-		$relation = $this->getRelation($name);
-
-		if ($relation->via !== null) {
-			if (is_array($relation->via)) {
-				/** @var ActiveRelation $viaRelation */
-				list($viaName, $viaRelation) = $relation->via;
-				$viaClass = $viaRelation->modelClass;
-				unset($this->_related[$viaName]);
-			} else {
-				$viaRelation = $relation->via;
-				$viaTable = reset($relation->via->from);
-			}
-			$columns = [];
-			foreach ($viaRelation->link as $a => $b) {
-				$columns[$a] = $this->$b;
-			}
-			foreach ($relation->link as $a => $b) {
-				$columns[$b] = $model->$a;
-			}
-			if (is_array($relation->via)) {
-				/** @var $viaClass ActiveRecord */
-				if ($delete) {
-					$viaClass::deleteAll($columns);
-				} else {
-					$nulls = [];
-					foreach (array_keys($columns) as $a) {
-						$nulls[$a] = null;
-					}
-					$viaClass::updateAll($nulls, $columns);
-				}
-			} else {
-				/** @var $viaTable string */
-				$command = static::getDb()->createCommand();
-				if ($delete) {
-					$command->delete($viaTable, $columns)->execute();
-				} else {
-					$nulls = [];
-					foreach (array_keys($columns) as $a) {
-						$nulls[$a] = null;
-					}
-					$command->update($viaTable, $nulls, $columns)->execute();
-				}
-			}
-		} else {
-			$p1 = $model->isPrimaryKey(array_keys($relation->link));
-			$p2 = $this->isPrimaryKey(array_values($relation->link));
-			if ($p1 && $p2 || $p2) {
-				foreach ($relation->link as $a => $b) {
-					$model->$a = null;
-				}
-				$delete ? $model->delete() : $model->save(false);
-			} elseif ($p1) {
-				foreach ($relation->link as $b) {
-					$this->$b = null;
-				}
-				$delete ? $this->delete() : $this->save(false);
-			} else {
-				throw new InvalidCallException('Unable to unlink models: the link does not involve any primary key.');
-			}
-		}
-
-		if (!$relation->multiple) {
-			unset($this->_related[$name]);
-		} elseif (isset($this->_related[$name])) {
-			/** @var ActiveRecord $b */
-			foreach ($this->_related[$name] as $a => $b) {
-				if ($model->getPrimaryKey() == $b->getPrimaryKey()) {
-					unset($this->_related[$name][$a]);
-				}
-			}
-		}
-	}
-
-	/**
-	 * @param array $link
-	 * @param ActiveRecord $foreignModel
-	 * @param ActiveRecord $primaryModel
-	 * @throws InvalidCallException
-	 */
-	private function bindModels($link, $foreignModel, $primaryModel)
-	{
-		foreach ($link as $fk => $pk) {
-			$value = $primaryModel->$pk;
-			if ($value === null) {
-				throw new InvalidCallException('Unable to link models: the primary key of ' . get_class($primaryModel) . ' is null.');
-			}
-			$foreignModel->$fk = $value;
-		}
-		$foreignModel->save(false);
-	}
-
-	/**
-	 * Returns a value indicating whether the given set of attributes represents the primary key for this model
-	 * @param array $keys the set of attributes to check
-	 * @return boolean whether the given set of attributes represents the primary key for this model
-	 */
-	public static function isPrimaryKey($keys)
-	{
-		$pks = static::primaryKey();
-		foreach ($keys as $key) {
-			if (!in_array($key, $pks, true)) {
-				return false;
-			}
-		}
-		return count($keys) === count($pks);
-	}
-
-	/**
 	 * Returns a value indicating whether the specified operation is transactional in the current [[scenario]].
 	 * @param integer $operation the operation to check. Possible values are [[OP_INSERT]], [[OP_UPDATE]] and [[OP_DELETE]].
 	 * @return boolean whether the specified operation is transactional in the current [[scenario]].
diff --git a/framework/yii/db/ActiveRecordInterface.php b/framework/yii/db/ActiveRecordInterface.php
new file mode 100644
index 0000000..4965a26
--- /dev/null
+++ b/framework/yii/db/ActiveRecordInterface.php
@@ -0,0 +1,279 @@
+<?php
+/**
+ * 
+ * 
+ * @author Carsten Brandt <mail@cebe.cc>
+ */
+
+namespace yii\db;
+
+/**
+ * ActiveRecordInterface
+ *
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @author Carsten Brandt <mail@cebe.cc>
+ * @since 2.0
+ */
+interface ActiveRecordInterface
+{
+	/**
+	 * Returns the primary key **name(s)** for this AR class.
+	 *
+	 * Note that an array should be returned even when the record only has a single primary key.
+	 *
+	 * For the primary key **value** see [[getPrimaryKey()]] instead.
+	 *
+	 * @return string[] the primary key name(s) for this AR class.
+	 */
+	public static function primaryKey();
+
+	/**
+	 * Returns the list of all attribute names of the record.
+	 * @return array list of attribute names.
+	 */
+	public function attributes();
+
+	/**
+	 * Returns the named attribute value.
+	 * If this record is the result of a query and the attribute is not loaded,
+	 * null will be returned.
+	 * @param string $name the attribute name
+	 * @return mixed the attribute value. Null if the attribute is not set or does not exist.
+	 * @see hasAttribute()
+	 */
+	public function getAttribute($name);
+
+	/**
+	 * Sets the named attribute value.
+	 * @param string $name the attribute name.
+	 * @param mixed $value the attribute value.
+	 * @see hasAttribute()
+	 */
+	public function setAttribute($name, $value);
+
+	/**
+	 * Returns a value indicating whether the record has an attribute with the specified name.
+	 * @param string $name the name of the attribute
+	 * @return boolean whether the record has an attribute with the specified name.
+	 */
+	public function hasAttribute($name);
+
+	/**
+	 * Returns the primary key value(s).
+	 * @param boolean $asArray whether to return the primary key value as an array. If true,
+	 * the return value will be an array with attribute names as keys and attribute values as values.
+	 * Note that for composite primary keys, an array will always be returned regardless of this parameter value.
+	 * @return mixed the primary key value. An array (attribute name => attribute value) is returned if the primary key
+	 * is composite or `$asArray` is true. A string is returned otherwise (null will be returned if
+	 * the key value is null).
+	 */
+	public function getPrimaryKey($asArray = false);
+
+	/**
+	 * Creates an [[ActiveQueryInterface|ActiveQuery]] instance for query purpose.
+	 *
+	 * This method is usually ment to be used like this:
+	 *
+	 * ```php
+	 * Customer::find(1); // find one customer by primary key
+	 * Customer::find()->all(); // find all customers
+	 * ```
+	 *
+	 * @param mixed $q the query parameter. This can be one of the followings:
+	 *
+	 *  - a scalar value (integer or string): query by a single primary key value and return the
+	 *    corresponding record.
+	 *  - an array of name-value pairs: query by a set of attribute values and return a single record matching all of them.
+	 *  - null (not specified): return a new [[ActiveQuery]] object for further query purpose.
+	 *
+	 * @return ActiveQueryInterface|static|null When `$q` is null, a new [[ActiveQuery]] instance
+	 * is returned; when `$q` is a scalar or an array, an ActiveRecord object matching it will be
+	 * returned (null will be returned if there is no matching).
+	 */
+	public static function find($q = null);
+
+	/**
+	 * Creates an [[ActiveQueryInterface|ActiveQuery]] instance.
+	 * This method is called by [[find()]] to start a SELECT query.
+	 * You may override this method to return a customized query (e.g. `CustomerQuery` specified
+	 * written for querying `Customer` purpose.)
+	 * @return ActiveQueryInterface the newly created [[ActiveQueryInterface|ActiveQuery]] instance.
+	 */
+	public static function createQuery();
+
+	/**
+	 * Updates records using the provided attribute values and conditions.
+	 * For example, to change the status to be 1 for all customers whose status is 2:
+	 *
+	 * ~~~
+	 * Customer::updateAll(['status' => 1], ['status' => '2']);
+	 * ~~~
+	 *
+	 * @param array $attributes attribute values (name-value pairs) to be saved for the record.
+	 * Unlike [[update()]] these are not going to be validated.
+	 * @param array $condition the condition that matches the records that should get updated.
+	 * Please refer to [[QueryInterface::where()]] on how to specify this parameter.
+	 * An empty condition will match all records.
+	 * @return integer the number of rows updated
+	 */
+	public static function updateAll($attributes, $condition = null);
+
+	/**
+	 * Deletes records using the provided conditions.
+	 * WARNING: If you do not specify any condition, this method will delete ALL rows in the table.
+	 *
+	 * For example, to delete all customers whose status is 3:
+	 *
+	 * ~~~
+	 * Customer::deleteAll([status = 3]);
+	 * ~~~
+	 *
+	 * @param array $condition the condition that matches the records that should get deleted.
+	 * Please refer to [[QueryInterface::where()]] on how to specify this parameter.
+	 * An empty condition will match all records.
+	 * @return integer the number of rows deleted
+	 */
+	public static function deleteAll($condition = null);
+
+	/**
+	 * Saves the current record.
+	 *
+	 * This method will call [[insert()]] when [[isNewRecord]] is true, or [[update()]]
+	 * when [[isNewRecord]] is false.
+	 *
+	 * For example, to save a customer record:
+	 *
+	 * ~~~
+	 * $customer = new Customer; // or $customer = Customer::find($id);
+	 * $customer->name = $name;
+	 * $customer->email = $email;
+	 * $customer->save();
+	 * ~~~
+	 *
+	 * @param boolean $runValidation whether to perform validation before saving the record.
+	 * If the validation fails, the record will not be saved to database. `false` will be returned
+	 * in this case.
+	 * @param array $attributes list of attributes that need to be saved. Defaults to null,
+	 * meaning all attributes that are loaded from DB will be saved.
+	 * @return boolean whether the saving succeeds
+	 */
+	public function save($runValidation = true, $attributes = null);
+
+	/**
+	 * Inserts the record into the database using the attribute values of this record.
+	 *
+	 * Usage example:
+	 *
+	 * ```php
+	 * $customer = new Customer;
+	 * $customer->name = $name;
+	 * $customer->email = $email;
+	 * $customer->insert();
+	 * ```
+	 *
+	 * @param boolean $runValidation whether to perform validation before saving the record.
+	 * If the validation fails, the record will not be inserted into the database.
+	 * @param array $attributes list of attributes that need to be saved. Defaults to null,
+	 * meaning all attributes that are loaded from DB will be saved.
+	 * @return boolean whether the attributes are valid and the record is inserted successfully.
+	 */
+	public function insert($runValidation = true, $attributes = null);
+
+	/**
+	 * Saves the changes to this active record into the database.
+	 *
+	 * Usage example:
+	 *
+	 * ```php
+	 * $customer = Customer::find($id);
+	 * $customer->name = $name;
+	 * $customer->email = $email;
+	 * $customer->update();
+	 * ```
+	 *
+	 * @param boolean $runValidation whether to perform validation before saving the record.
+	 * If the validation fails, the record will not be inserted into the database.
+	 * @param array $attributes list of attributes that need to be saved. Defaults to null,
+	 * meaning all attributes that are loaded from DB will be saved.
+	 * @return integer|boolean the number of rows affected, or false if validation fails
+	 * or updating process is stopped for other reasons.
+	 * Note that it is possible that the number of rows affected is 0, even though the
+	 * update execution is successful.
+	 */
+	public function update($runValidation = true, $attributes = null);
+
+	/**
+	 * Deletes the record from the database.
+	 *
+	 * @return integer|boolean the number of rows deleted, or false if the deletion is unsuccessful for some reason.
+	 * Note that it is possible that the number of rows deleted is 0, even though the deletion execution is successful.
+	 */
+	public function delete();
+
+	/**
+	 * Returns a value indicating whether the current record is new (not saved in the database).
+	 * @return boolean whether the record is new and should be inserted when calling [[save()]].
+	 */
+	public function getIsNewRecord();
+
+	/**
+	 * Returns a value indicating whether the given active record is the same as the current one.
+	 * Two [[isNewRecord|new]] records are considered to be not equal.
+	 * @param static $record record to compare to
+	 * @return boolean whether the two active records refer to the same row in the same database table.
+	 */
+	public function equals($record);
+
+	/**
+	 * Creates an [[ActiveRelationInterface|ActiveRelation]] instance.
+	 * This method is called by [[BaseActiveRecord::hasOne()]] and [[BaseActiveRecord::hasMany()]] to
+	 * create a relation instance.
+	 * You may override this method to return a customized relation.
+	 * @param array $config the configuration passed to the ActiveRelation class.
+	 * @return ActiveRelation the newly created [[ActiveRelation]] instance.
+	 */
+	public static function createActiveRelation($config = []);
+
+	/**
+	 * Returns the relation object with the specified name.
+	 * A relation is defined by a getter method which returns an [[ActiveRelationInterface|ActiveRelation]] object.
+	 * It can be declared in either the ActiveRecord class itself or one of its behaviors.
+	 * @param string $name the relation name
+	 * @return ActiveRelation the relation object
+	 */
+	public function getRelation($name);
+
+	/**
+	 * Establishes the relationship between two records.
+	 *
+	 * The relationship is established by setting the foreign key value(s) in one record
+	 * to be the corresponding primary key value(s) in the other record.
+	 * The record with the foreign key will be saved into database without performing validation.
+	 *
+	 * If the relationship involves a pivot table, a new row will be inserted into the
+	 * pivot table which contains the primary key values from both records.
+	 *
+	 * This method requires that the primary key value is not null.
+	 *
+	 * @param string $name the case sensitive name of the relationship.
+	 * @param static $model the record to be linked with the current one.
+	 * @param array $extraColumns additional column values to be saved into the pivot table.
+	 * This parameter is only meaningful for a relationship involving a pivot table
+	 * (i.e., a relation set with `[[ActiveRelationInterface::via()]]`.)
+	 */
+	public function link($name, $model, $extraColumns = []);
+
+	/**
+	 * Destroys the relationship between two records.
+	 *
+	 * The record with the foreign key of the relationship will be deleted if `$delete` is true.
+	 * Otherwise, the foreign key will be set null and the record will be saved without validation.
+	 *
+	 * @param string $name the case sensitive name of the relationship.
+	 * @param static $model the model to be unlinked from the current one.
+	 * @param boolean $delete whether to delete the model that contains the foreign key.
+	 * If false, the model's foreign key will be set null and saved.
+	 * If true, the model containing the foreign key will be deleted.
+	 */
+	public function unlink($name, $model, $delete = false);
+}
\ No newline at end of file
diff --git a/framework/yii/db/ActiveRelationTrait.php b/framework/yii/db/ActiveRelationTrait.php
index 2960196..832bb62 100644
--- a/framework/yii/db/ActiveRelationTrait.php
+++ b/framework/yii/db/ActiveRelationTrait.php
@@ -104,7 +104,7 @@ trait ActiveRelationTrait
 		if (count($primaryModels) === 1 && !$this->multiple) {
 			$model = $this->one();
 			foreach ($primaryModels as $i => $primaryModel) {
-				if ($primaryModel instanceof ActiveRecord) {
+				if ($primaryModel instanceof ActiveRecordInterface) {
 					$primaryModel->populateRelation($name, $model);
 				} else {
 					$primaryModels[$i][$name] = $model;
@@ -123,7 +123,7 @@ trait ActiveRelationTrait
 			foreach ($primaryModels as $i => $primaryModel) {
 				$key = $this->getModelKey($primaryModel, $link);
 				$value = isset($buckets[$key]) ? $buckets[$key] : ($this->multiple ? [] : null);
-				if ($primaryModel instanceof ActiveRecord) {
+				if ($primaryModel instanceof ActiveRecordInterface) {
 					$primaryModel->populateRelation($name, $value);
 				} else {
 					$primaryModels[$i][$name] = $value;
diff --git a/framework/yii/db/BaseActiveRecord.php b/framework/yii/db/BaseActiveRecord.php
new file mode 100644
index 0000000..00360c4
--- /dev/null
+++ b/framework/yii/db/BaseActiveRecord.php
@@ -0,0 +1,1229 @@
+<?php
+/**
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @link http://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license http://www.yiiframework.com/license/
+ */
+
+namespace yii\db;
+
+use yii\base\InvalidConfigException;
+use yii\base\Model;
+use yii\base\InvalidParamException;
+use yii\base\ModelEvent;
+use yii\base\NotSupportedException;
+use yii\base\UnknownMethodException;
+use yii\base\InvalidCallException;
+use yii\helpers\StringHelper;
+use yii\helpers\Inflector;
+
+/**
+ * ActiveRecord is the base class for classes representing relational data in terms of objects.
+ *
+ * @include @yii/db/ActiveRecord.md
+ *
+ * @property array $dirtyAttributes The changed attribute values (name-value pairs). This property is
+ * read-only.
+ * @property boolean $isNewRecord Whether the record is new and should be inserted when calling [[save()]].
+ * @property array $oldAttributes The old attribute values (name-value pairs).
+ * @property mixed $oldPrimaryKey The old primary key value. An array (column name => column value) is
+ * returned if the primary key is composite. A string is returned otherwise (null will be returned if the key
+ * value is null). This property is read-only.
+ * @property array $populatedRelations An array of relation data indexed by relation names. This property is
+ * read-only.
+ * @property mixed $primaryKey The primary key value. An array (column name => column value) is returned if
+ * the primary key is composite. A string is returned otherwise (null will be returned if the key value is null).
+ * This property is read-only.
+ *
+ * @author Qiang Xue <qiang.xue@gmail.com>
+ * @author Carsten Brandt <mail@cebe.cc>
+ * @since 2.0
+ */
+abstract class BaseActiveRecord extends Model implements ActiveRecordInterface
+{
+	/**
+	 * @event Event an event that is triggered when the record is initialized via [[init()]].
+	 */
+	const EVENT_INIT = 'init';
+	/**
+	 * @event Event an event that is triggered after the record is created and populated with query result.
+	 */
+	const EVENT_AFTER_FIND = 'afterFind';
+	/**
+	 * @event ModelEvent an event that is triggered before inserting a record.
+	 * You may set [[ModelEvent::isValid]] to be false to stop the insertion.
+	 */
+	const EVENT_BEFORE_INSERT = 'beforeInsert';
+	/**
+	 * @event Event an event that is triggered after a record is inserted.
+	 */
+	const EVENT_AFTER_INSERT = 'afterInsert';
+	/**
+	 * @event ModelEvent an event that is triggered before updating a record.
+	 * You may set [[ModelEvent::isValid]] to be false to stop the update.
+	 */
+	const EVENT_BEFORE_UPDATE = 'beforeUpdate';
+	/**
+	 * @event Event an event that is triggered after a record is updated.
+	 */
+	const EVENT_AFTER_UPDATE = 'afterUpdate';
+	/**
+	 * @event ModelEvent an event that is triggered before deleting a record.
+	 * You may set [[ModelEvent::isValid]] to be false to stop the deletion.
+	 */
+	const EVENT_BEFORE_DELETE = 'beforeDelete';
+	/**
+	 * @event Event an event that is triggered after a record is deleted.
+	 */
+	const EVENT_AFTER_DELETE = 'afterDelete';
+
+	/**
+	 * @var array attribute values indexed by attribute names
+	 */
+	private $_attributes = [];
+	/**
+	 * @var array old attribute values indexed by attribute names.
+	 */
+	private $_oldAttributes;
+	/**
+	 * @var array related models indexed by the relation names
+	 */
+	private $_related = [];
+
+
+	/**
+	 * Creates an [[ActiveQuery]] instance for query purpose.
+	 *
+	 * @include @yii/db/ActiveRecord-find.md
+	 *
+	 * @param mixed $q the query parameter. This can be one of the followings:
+	 *
+	 *  - a scalar value (integer or string): query by a single primary key value and return the
+	 *    corresponding record.
+	 *  - an array of name-value pairs: query by a set of column values and return a single record matching all of them.
+	 *  - null: return a new [[ActiveQuery]] object for further query purpose.
+	 *
+	 * @return ActiveQuery|ActiveRecord|null When `$q` is null, a new [[ActiveQuery]] instance
+	 * is returned; when `$q` is a scalar or an array, an ActiveRecord object matching it will be
+	 * returned (null will be returned if there is no matching).
+	 * @throws InvalidConfigException if the AR class does not have a primary key
+	 * @see createQuery()
+	 */
+	public static function find($q = null)
+	{
+		$query = static::createQuery();
+		if (is_array($q)) {
+			return $query->where($q)->one();
+		} elseif ($q !== null) {
+			// query by primary key
+			$primaryKey = static::primaryKey();
+			if (isset($primaryKey[0])) {
+				return $query->where([$primaryKey[0] => $q])->one();
+			} else {
+				throw new InvalidConfigException(get_called_class() . ' must have a primary key.');
+			}
+		}
+		return $query;
+	}
+
+	/**
+	 * Updates the whole table using the provided attribute values and conditions.
+	 * For example, to change the status to be 1 for all customers whose status is 2:
+	 *
+	 * ~~~
+	 * Customer::updateAll(['status' => 1], 'status = 2');
+	 * ~~~
+	 *
+	 * @param array $attributes attribute values (name-value pairs) to be saved into the table
+	 * @param string|array $condition the conditions that will be put in the WHERE part of the UPDATE SQL.
+	 * Please refer to [[Query::where()]] on how to specify this parameter.
+	 * @param array $params the parameters (name => value) to be bound to the query.
+	 * @return integer the number of rows updated
+	 */
+	public static function updateAll($attributes, $condition = '')
+	{
+		throw new NotSupportedException(__METHOD__ . ' is not supported.');
+	}
+
+	/**
+	 * Updates the whole table using the provided counter changes and conditions.
+	 * For example, to increment all customers' age by 1,
+	 *
+	 * ~~~
+	 * Customer::updateAllCounters(['age' => 1]);
+	 * ~~~
+	 *
+	 * @param array $counters the counters to be updated (attribute name => increment value).
+	 * Use negative values if you want to decrement the counters.
+	 * @param string|array $condition the conditions that will be put in the WHERE part of the UPDATE SQL.
+	 * Please refer to [[Query::where()]] on how to specify this parameter.
+	 * @param array $params the parameters (name => value) to be bound to the query.
+	 * Do not name the parameters as `:bp0`, `:bp1`, etc., because they are used internally by this method.
+	 * @return integer the number of rows updated
+	 */
+	public static function updateAllCounters($counters, $condition = '')
+	{
+		throw new NotSupportedException(__METHOD__ . ' is not supported.');
+	}
+
+	/**
+	 * Deletes rows in the table using the provided conditions.
+	 * WARNING: If you do not specify any condition, this method will delete ALL rows in the table.
+	 *
+	 * For example, to delete all customers whose status is 3:
+	 *
+	 * ~~~
+	 * Customer::deleteAll('status = 3');
+	 * ~~~
+	 *
+	 * @param string|array $condition the conditions that will be put in the WHERE part of the DELETE SQL.
+	 * Please refer to [[Query::where()]] on how to specify this parameter.
+	 * @param array $params the parameters (name => value) to be bound to the query.
+	 * @return integer the number of rows deleted
+	 */
+	public static function deleteAll($condition = '', $params = [])
+	{
+		throw new NotSupportedException(__METHOD__ . ' is not supported.');
+	}
+
+	/**
+	 * Returns the name of the column that stores the lock version for implementing optimistic locking.
+	 *
+	 * Optimistic locking allows multiple users to access the same record for edits and avoids
+	 * potential conflicts. In case when a user attempts to save the record upon some staled data
+	 * (because another user has modified the data), a [[StaleObjectException]] exception will be thrown,
+	 * and the update or deletion is skipped.
+	 *
+	 * Optimistic locking is only supported by [[update()]] and [[delete()]].
+	 *
+	 * To use Optimistic locking:
+	 *
+	 * 1. Create a column to store the version number of each row. The column type should be `BIGINT DEFAULT 0`.
+	 *    Override this method to return the name of this column.
+	 * 2. In the Web form that collects the user input, add a hidden field that stores
+	 *    the lock version of the recording being updated.
+	 * 3. In the controller action that does the data updating, try to catch the [[StaleObjectException]]
+	 *    and implement necessary business logic (e.g. merging the changes, prompting stated data)
+	 *    to resolve the conflict.
+	 *
+	 * @return string the column name that stores the lock version of a table row.
+	 * If null is returned (default implemented), optimistic locking will not be supported.
+	 */
+	public function optimisticLock()
+	{
+		return null;
+	}
+
+	/**
+	 * PHP getter magic method.
+	 * This method is overridden so that attributes and related objects can be accessed like properties.
+	 * @param string $name property name
+	 * @return mixed property value
+	 * @see getAttribute()
+	 */
+	public function __get($name)
+	{
+		if (isset($this->_attributes[$name]) || array_key_exists($name, $this->_attributes)) {
+			return $this->_attributes[$name];
+		} elseif ($this->hasAttribute($name)) {
+			return null;
+		} else {
+			if (isset($this->_related[$name]) || array_key_exists($name, $this->_related)) {
+				return $this->_related[$name];
+			}
+			$value = parent::__get($name);
+			if ($value instanceof ActiveRelationInterface) {
+				return $this->_related[$name] = $value->multiple ? $value->all() : $value->one();
+			} else {
+				return $value;
+			}
+		}
+	}
+
+	/**
+	 * PHP setter magic method.
+	 * This method is overridden so that AR attributes can be accessed like properties.
+	 * @param string $name property name
+	 * @param mixed $value property value
+	 */
+	public function __set($name, $value)
+	{
+		if ($this->hasAttribute($name)) {
+			$this->_attributes[$name] = $value;
+		} else {
+			parent::__set($name, $value);
+		}
+	}
+
+	/**
+	 * Checks if a property value is null.
+	 * This method overrides the parent implementation by checking if the named attribute is null or not.
+	 * @param string $name the property name or the event name
+	 * @return boolean whether the property value is null
+	 */
+	public function __isset($name)
+	{
+		try {
+			return $this->__get($name) !== null;
+		} catch (\Exception $e) {
+			return false;
+		}
+	}
+
+	/**
+	 * Sets a component property to be null.
+	 * This method overrides the parent implementation by clearing
+	 * the specified attribute value.
+	 * @param string $name the property name or the event name
+	 */
+	public function __unset($name)
+	{
+		if ($this->hasAttribute($name)) {
+			unset($this->_attributes[$name]);
+		} else {
+			if (isset($this->_related[$name])) {
+				unset($this->_related[$name]);
+			} else {
+				parent::__unset($name);
+			}
+		}
+	}
+
+	/**
+	 * Declares a `has-one` relation.
+	 * The declaration is returned in terms of an [[ActiveRelation]] instance
+	 * through which the related record can be queried and retrieved back.
+	 *
+	 * A `has-one` relation means that there is at most one related record matching
+	 * the criteria set by this relation, e.g., a customer has one country.
+	 *
+	 * For example, to declare the `country` relation for `Customer` class, we can write
+	 * the following code in the `Customer` class:
+	 *
+	 * ~~~
+	 * public function getCountry()
+	 * {
+	 *     return $this->hasOne(Country::className(), ['id' => 'country_id']);
+	 * }
+	 * ~~~
+	 *
+	 * Note that in the above, the 'id' key in the `$link` parameter refers to an attribute name
+	 * in the related class `Country`, while the 'country_id' value refers to an attribute name
+	 * in the current AR class.
+	 *
+	 * Call methods declared in [[ActiveRelation]] to further customize the relation.
+	 *
+	 * @param string $class the class name of the related record
+	 * @param array $link the primary-foreign key constraint. The keys of the array refer to
+	 * the attributes of the record associated with the `$class` model, while the values of the
+	 * array refer to the corresponding attributes in **this** AR class.
+	 * @return ActiveRelationInterface the relation object.
+	 */
+	public function hasOne($class, $link)
+	{
+		/** @var ActiveRecord $class */
+		return $class::createActiveRelation([
+			'modelClass' => $class,
+			'primaryModel' => $this,
+			'link' => $link,
+			'multiple' => false,
+		]);
+	}
+
+	/**
+	 * Declares a `has-many` relation.
+	 * The declaration is returned in terms of an [[ActiveRelation]] instance
+	 * through which the related record can be queried and retrieved back.
+	 *
+	 * A `has-many` relation means that there are multiple related records matching
+	 * the criteria set by this relation, e.g., a customer has many orders.
+	 *
+	 * For example, to declare the `orders` relation for `Customer` class, we can write
+	 * the following code in the `Customer` class:
+	 *
+	 * ~~~
+	 * public function getOrders()
+	 * {
+	 *     return $this->hasMany(Order::className(), ['customer_id' => 'id']);
+	 * }
+	 * ~~~
+	 *
+	 * Note that in the above, the 'customer_id' key in the `$link` parameter refers to
+	 * an attribute name in the related class `Order`, while the 'id' value refers to
+	 * an attribute name in the current AR class.
+	 *
+	 * @param string $class the class name of the related record
+	 * @param array $link the primary-foreign key constraint. The keys of the array refer to
+	 * the attributes of the record associated with the `$class` model, while the values of the
+	 * array refer to the corresponding attributes in **this** AR class.
+	 * @return ActiveRelationInterface the relation object.
+	 */
+	public function hasMany($class, $link)
+	{
+		/** @var ActiveRecord $class */
+		return $class::createActiveRelation([
+			'modelClass' => $class,
+			'primaryModel' => $this,
+			'link' => $link,
+			'multiple' => true,
+		]);
+	}
+
+	/**
+	 * Populates the named relation with the related records.
+	 * Note that this method does not check if the relation exists or not.
+	 * @param string $name the relation name (case-sensitive)
+	 * @param ActiveRecord|array|null the related records to be populated into the relation.
+	 */
+	public function populateRelation($name, $records)
+	{
+		$this->_related[$name] = $records;
+	}
+
+	/**
+	 * Check whether the named relation has been populated with records.
+	 * @param string $name the relation name (case-sensitive)
+	 * @return bool whether relation has been populated with records.
+	 */
+	public function isRelationPopulated($name)
+	{
+		return array_key_exists($name, $this->_related);
+	}
+
+	/**
+	 * Returns all populated relations.
+	 * @return array an array of relation data indexed by relation names.
+	 */
+	public function getPopulatedRelations()
+	{
+		return $this->_related;
+	}
+
+	/**
+	 * Returns a value indicating whether the model has an attribute with the specified name.
+	 * @param string $name the name of the attribute
+	 * @return boolean whether the model has an attribute with the specified name.
+	 */
+	public function hasAttribute($name)
+	{
+		return isset($this->_attributes[$name]) || in_array($name, $this->attributes());
+	}
+
+	/**
+	 * Returns the named attribute value.
+	 * If this record is the result of a query and the attribute is not loaded,
+	 * null will be returned.
+	 * @param string $name the attribute name
+	 * @return mixed the attribute value. Null if the attribute is not set or does not exist.
+	 * @see hasAttribute()
+	 */
+	public function getAttribute($name)
+	{
+		return isset($this->_attributes[$name]) ? $this->_attributes[$name] : null;
+	}
+
+	/**
+	 * Sets the named attribute value.
+	 * @param string $name the attribute name
+	 * @param mixed $value the attribute value.
+	 * @throws InvalidParamException if the named attribute does not exist.
+	 * @see hasAttribute()
+	 */
+	public function setAttribute($name, $value)
+	{
+		if ($this->hasAttribute($name)) {
+			$this->_attributes[$name] = $value;
+		} else {
+			throw new InvalidParamException(get_class($this) . ' has no attribute named "' . $name . '".');
+		}
+	}
+
+	/**
+	 * Returns the old attribute values.
+	 * @return array the old attribute values (name-value pairs)
+	 */
+	public function getOldAttributes()
+	{
+		return $this->_oldAttributes === null ? [] : $this->_oldAttributes;
+	}
+
+	/**
+	 * Sets the old attribute values.
+	 * All existing old attribute values will be discarded.
+	 * @param array $values old attribute values to be set.
+	 */
+	public function setOldAttributes($values)
+	{
+		$this->_oldAttributes = $values;
+	}
+
+	/**
+	 * Returns the old value of the named attribute.
+	 * If this record is the result of a query and the attribute is not loaded,
+	 * null will be returned.
+	 * @param string $name the attribute name
+	 * @return mixed the old attribute value. Null if the attribute is not loaded before
+	 * or does not exist.
+	 * @see hasAttribute()
+	 */
+	public function getOldAttribute($name)
+	{
+		return isset($this->_oldAttributes[$name]) ? $this->_oldAttributes[$name] : null;
+	}
+
+	/**
+	 * Sets the old value of the named attribute.
+	 * @param string $name the attribute name
+	 * @param mixed $value the old attribute value.
+	 * @throws InvalidParamException if the named attribute does not exist.
+	 * @see hasAttribute()
+	 */
+	public function setOldAttribute($name, $value)
+	{
+		if (isset($this->_oldAttributes[$name]) || $this->hasAttribute($name)) {
+			$this->_oldAttributes[$name] = $value;
+		} else {
+			throw new InvalidParamException(get_class($this) . ' has no attribute named "' . $name . '".');
+		}
+	}
+
+	/**
+	 * Returns a value indicating whether the named attribute has been changed.
+	 * @param string $name the name of the attribute
+	 * @return boolean whether the attribute has been changed
+	 */
+	public function isAttributeChanged($name)
+	{
+		if (isset($this->_attributes[$name], $this->_oldAttributes[$name])) {
+			return $this->_attributes[$name] !== $this->_oldAttributes[$name];
+		} else {
+			return isset($this->_attributes[$name]) || isset($this->_oldAttributes[$name]);
+		}
+	}
+
+	/**
+	 * Returns the attribute values that have been modified since they are loaded or saved most recently.
+	 * @param string[]|null $names the names of the attributes whose values may be returned if they are
+	 * changed recently. If null, [[attributes()]] will be used.
+	 * @return array the changed attribute values (name-value pairs)
+	 */
+	public function getDirtyAttributes($names = null)
+	{
+		if ($names === null) {
+			$names = $this->attributes();
+		}
+		$names = array_flip($names);
+		$attributes = [];
+		if ($this->_oldAttributes === null) {
+			foreach ($this->_attributes as $name => $value) {
+				if (isset($names[$name])) {
+					$attributes[$name] = $value;
+				}
+			}
+		} else {
+			foreach ($this->_attributes as $name => $value) {
+				if (isset($names[$name]) && (!array_key_exists($name, $this->_oldAttributes) || $value !== $this->_oldAttributes[$name])) {
+					$attributes[$name] = $value;
+				}
+			}
+		}
+		return $attributes;
+	}
+
+	/**
+	 * Saves the current record.
+	 *
+	 * This method will call [[insert()]] when [[isNewRecord]] is true, or [[update()]]
+	 * when [[isNewRecord]] is false.
+	 *
+	 * For example, to save a customer record:
+	 *
+	 * ~~~
+	 * $customer = new Customer;  // or $customer = Customer::find($id);
+	 * $customer->name = $name;
+	 * $customer->email = $email;
+	 * $customer->save();
+	 * ~~~
+	 *
+	 *
+	 * @param boolean $runValidation whether to perform validation before saving the record.
+	 * If the validation fails, the record will not be saved to database.
+	 * @param array $attributes list of attributes that need to be saved. Defaults to null,
+	 * meaning all attributes that are loaded from DB will be saved.
+	 * @return boolean whether the saving succeeds
+	 */
+	public function save($runValidation = true, $attributes = null)
+	{
+		if ($this->getIsNewRecord()) {
+			return $this->insert($runValidation, $attributes);
+		} else {
+			return $this->update($runValidation, $attributes) !== false;
+		}
+	}
+
+	/**
+	 * Saves the changes to this active record into the associated database table.
+	 *
+	 * This method performs the following steps in order:
+	 *
+	 * 1. call [[beforeValidate()]] when `$runValidation` is true. If validation
+	 *    fails, it will skip the rest of the steps;
+	 * 2. call [[afterValidate()]] when `$runValidation` is true.
+	 * 3. call [[beforeSave()]]. If the method returns false, it will skip the
+	 *    rest of the steps;
+	 * 4. save the record into database. If this fails, it will skip the rest of the steps;
+	 * 5. call [[afterSave()]];
+	 *
+	 * In the above step 1, 2, 3 and 5, events [[EVENT_BEFORE_VALIDATE]],
+	 * [[EVENT_BEFORE_UPDATE]], [[EVENT_AFTER_UPDATE]] and [[EVENT_AFTER_VALIDATE]]
+	 * will be raised by the corresponding methods.
+	 *
+	 * Only the [[changedAttributes|changed attribute values]] will be saved into database.
+	 *
+	 * For example, to update a customer record:
+	 *
+	 * ~~~
+	 * $customer = Customer::find($id);
+	 * $customer->name = $name;
+	 * $customer->email = $email;
+	 * $customer->update();
+	 * ~~~
+	 *
+	 * Note that it is possible the update does not affect any row in the table.
+	 * In this case, this method will return 0. For this reason, you should use the following
+	 * code to check if update() is successful or not:
+	 *
+	 * ~~~
+	 * if ($this->update() !== false) {
+	 *     // update successful
+	 * } else {
+	 *     // update failed
+	 * }
+	 * ~~~
+	 *
+	 * @param boolean $runValidation whether to perform validation before saving the record.
+	 * If the validation fails, the record will not be inserted into the database.
+	 * @param array $attributes list of attributes that need to be saved. Defaults to null,
+	 * meaning all attributes that are loaded from DB will be saved.
+	 * @return integer|boolean the number of rows affected, or false if validation fails
+	 * or [[beforeSave()]] stops the updating process.
+	 * @throws StaleObjectException if [[optimisticLock|optimistic locking]] is enabled and the data
+	 * being updated is outdated.
+	 * @throws \Exception in case update failed.
+	 */
+	public function update($runValidation = true, $attributes = null)
+	{
+		if ($runValidation && !$this->validate($attributes)) {
+			return false;
+		}
+		return $this->updateInternal($attributes);
+	}
+
+	/**
+	 * @see CActiveRecord::update()
+	 * @throws StaleObjectException
+	 */
+	protected function updateInternal($attributes = null)
+	{
+		if (!$this->beforeSave(false)) {
+			return false;
+		}
+		$values = $this->getDirtyAttributes($attributes);
+		if (empty($values)) {
+			$this->afterSave(false);
+			return 0;
+		}
+		$condition = $this->getOldPrimaryKey(true);
+		$lock = $this->optimisticLock();
+		if ($lock !== null) {
+			if (!isset($values[$lock])) {
+				$values[$lock] = $this->$lock + 1;
+			}
+			$condition[$lock] = $this->$lock;
+		}
+		// We do not check the return value of updateAll() because it's possible
+		// that the UPDATE statement doesn't change anything and thus returns 0.
+		$rows = $this->updateAll($values, $condition);
+
+		if ($lock !== null && !$rows) {
+			throw new StaleObjectException('The object being updated is outdated.');
+		}
+
+		foreach ($values as $name => $value) {
+			$this->_oldAttributes[$name] = $this->_attributes[$name];
+		}
+		$this->afterSave(false);
+		return $rows;
+	}
+
+	/**
+	 * Updates one or several counter columns for the current AR object.
+	 * Note that this method differs from [[updateAllCounters()]] in that it only
+	 * saves counters for the current AR object.
+	 *
+	 * An example usage is as follows:
+	 *
+	 * ~~~
+	 * $post = Post::find($id);
+	 * $post->updateCounters(['view_count' => 1]);
+	 * ~~~
+	 *
+	 * @param array $counters the counters to be updated (attribute name => increment value)
+	 * Use negative values if you want to decrement the counters.
+	 * @return boolean whether the saving is successful
+	 * @see updateAllCounters()
+	 */
+	public function updateCounters($counters)
+	{
+		if ($this->updateAllCounters($counters, $this->getOldPrimaryKey(true)) > 0) {
+			foreach ($counters as $name => $value) {
+				$this->_attributes[$name] += $value;
+				$this->_oldAttributes[$name] = $this->_attributes[$name];
+			}
+			return true;
+		} else {
+			return false;
+		}
+	}
+
+	/**
+	 * Deletes the table row corresponding to this active record.
+	 *
+	 * This method performs the following steps in order:
+	 *
+	 * 1. call [[beforeDelete()]]. If the method returns false, it will skip the
+	 *    rest of the steps;
+	 * 2. delete the record from the database;
+	 * 3. call [[afterDelete()]].
+	 *
+	 * In the above step 1 and 3, events named [[EVENT_BEFORE_DELETE]] and [[EVENT_AFTER_DELETE]]
+	 * will be raised by the corresponding methods.
+	 *
+	 * @return integer|boolean the number of rows deleted, or false if the deletion is unsuccessful for some reason.
+	 * Note that it is possible the number of rows deleted is 0, even though the deletion execution is successful.
+	 * @throws StaleObjectException if [[optimisticLock|optimistic locking]] is enabled and the data
+	 * being deleted is outdated.
+	 * @throws \Exception in case delete failed.
+	 */
+	public function delete()
+	{
+		$result = false;
+		if ($this->beforeDelete()) {
+			// we do not check the return value of deleteAll() because it's possible
+			// the record is already deleted in the database and thus the method will return 0
+			$condition = $this->getOldPrimaryKey(true);
+			$lock = $this->optimisticLock();
+			if ($lock !== null) {
+				$condition[$lock] = $this->$lock;
+			}
+			$result = $this->deleteAll($condition);
+			if ($lock !== null && !$result) {
+				throw new StaleObjectException('The object being deleted is outdated.');
+			}
+			$this->_oldAttributes = null;
+			$this->afterDelete();
+		}
+		return $result;
+	}
+
+	/**
+	 * Returns a value indicating whether the current record is new.
+	 * @return boolean whether the record is new and should be inserted when calling [[save()]].
+	 */
+	public function getIsNewRecord()
+	{
+		return $this->_oldAttributes === null;
+	}
+
+	/**
+	 * Sets the value indicating whether the record is new.
+	 * @param boolean $value whether the record is new and should be inserted when calling [[save()]].
+	 * @see getIsNewRecord()
+	 */
+	public function setIsNewRecord($value)
+	{
+		$this->_oldAttributes = $value ? null : $this->_attributes;
+	}
+
+	/**
+	 * Initializes the object.
+	 * This method is called at the end of the constructor.
+	 * The default implementation will trigger an [[EVENT_INIT]] event.
+	 * If you override this method, make sure you call the parent implementation at the end
+	 * to ensure triggering of the event.
+	 */
+	public function init()
+	{
+		parent::init();
+		$this->trigger(self::EVENT_INIT);
+	}
+
+	/**
+	 * This method is called when the AR object is created and populated with the query result.
+	 * The default implementation will trigger an [[EVENT_AFTER_FIND]] event.
+	 * When overriding this method, make sure you call the parent implementation to ensure the
+	 * event is triggered.
+	 */
+	public function afterFind()
+	{
+		$this->trigger(self::EVENT_AFTER_FIND);
+	}
+
+	/**
+	 * This method is called at the beginning of inserting or updating a record.
+	 * The default implementation will trigger an [[EVENT_BEFORE_INSERT]] event when `$insert` is true,
+	 * or an [[EVENT_BEFORE_UPDATE]] event if `$insert` is false.
+	 * When overriding this method, make sure you call the parent implementation like the following:
+	 *
+	 * ~~~
+	 * public function beforeSave($insert)
+	 * {
+	 *     if (parent::beforeSave($insert)) {
+	 *         // ...custom code here...
+	 *         return true;
+	 *     } else {
+	 *         return false;
+	 *     }
+	 * }
+	 * ~~~
+	 *
+	 * @param boolean $insert whether this method called while inserting a record.
+	 * If false, it means the method is called while updating a record.
+	 * @return boolean whether the insertion or updating should continue.
+	 * If false, the insertion or updating will be cancelled.
+	 */
+	public function beforeSave($insert)
+	{
+		$event = new ModelEvent;
+		$this->trigger($insert ? self::EVENT_BEFORE_INSERT : self::EVENT_BEFORE_UPDATE, $event);
+		return $event->isValid;
+	}
+
+	/**
+	 * This method is called at the end of inserting or updating a record.
+	 * The default implementation will trigger an [[EVENT_AFTER_INSERT]] event when `$insert` is true,
+	 * or an [[EVENT_AFTER_UPDATE]] event if `$insert` is false.
+	 * When overriding this method, make sure you call the parent implementation so that
+	 * the event is triggered.
+	 * @param boolean $insert whether this method called while inserting a record.
+	 * If false, it means the method is called while updating a record.
+	 */
+	public function afterSave($insert)
+	{
+		$this->trigger($insert ? self::EVENT_AFTER_INSERT : self::EVENT_AFTER_UPDATE);
+	}
+
+	/**
+	 * This method is invoked before deleting a record.
+	 * The default implementation raises the [[EVENT_BEFORE_DELETE]] event.
+	 * When overriding this method, make sure you call the parent implementation like the following:
+	 *
+	 * ~~~
+	 * public function beforeDelete()
+	 * {
+	 *     if (parent::beforeDelete()) {
+	 *         // ...custom code here...
+	 *         return true;
+	 *     } else {
+	 *         return false;
+	 *     }
+	 * }
+	 * ~~~
+	 *
+	 * @return boolean whether the record should be deleted. Defaults to true.
+	 */
+	public function beforeDelete()
+	{
+		$event = new ModelEvent;
+		$this->trigger(self::EVENT_BEFORE_DELETE, $event);
+		return $event->isValid;
+	}
+
+	/**
+	 * This method is invoked after deleting a record.
+	 * The default implementation raises the [[EVENT_AFTER_DELETE]] event.
+	 * You may override this method to do postprocessing after the record is deleted.
+	 * Make sure you call the parent implementation so that the event is raised properly.
+	 */
+	public function afterDelete()
+	{
+		$this->trigger(self::EVENT_AFTER_DELETE);
+	}
+
+	/**
+	 * Repopulates this active record with the latest data.
+	 * @return boolean whether the row still exists in the database. If true, the latest data
+	 * will be populated to this active record. Otherwise, this record will remain unchanged.
+	 */
+	public function refresh()
+	{
+		$record = $this->find($this->getPrimaryKey(true));
+		if ($record === null) {
+			return false;
+		}
+		foreach ($this->attributes() as $name) {
+			$this->_attributes[$name] = isset($record->_attributes[$name]) ? $record->_attributes[$name] : null;
+		}
+		$this->_oldAttributes = $this->_attributes;
+		$this->_related = [];
+		return true;
+	}
+
+	/**
+	 * Returns a value indicating whether the given active record is the same as the current one.
+	 * The comparison is made by comparing the table names and the primary key values of the two active records.
+	 * If one of the records [[isNewRecord|is new]] they are also considered not equal.
+	 * @param ActiveRecord $record record to compare to
+	 * @return boolean whether the two active records refer to the same row in the same database table.
+	 */
+	public function equals($record)
+	{
+		if ($this->isNewRecord || $record->isNewRecord) {
+			return false;
+		}
+		return get_class($this) === get_class($record) && $this->getPrimaryKey() === $record->getPrimaryKey();
+	}
+
+	/**
+	 * Returns the primary key value(s).
+	 * @param boolean $asArray whether to return the primary key value as an array. If true,
+	 * the return value will be an array with column names as keys and column values as values.
+	 * Note that for composite primary keys, an array will always be returned regardless of this parameter value.
+	 * @property mixed The primary key value. An array (column name => column value) is returned if
+	 * the primary key is composite. A string is returned otherwise (null will be returned if
+	 * the key value is null).
+	 * @return mixed the primary key value. An array (column name => column value) is returned if the primary key
+	 * is composite or `$asArray` is true. A string is returned otherwise (null will be returned if
+	 * the key value is null).
+	 */
+	public function getPrimaryKey($asArray = false)
+	{
+		$keys = $this->primaryKey();
+		if (count($keys) === 1 && !$asArray) {
+			return isset($this->_attributes[$keys[0]]) ? $this->_attributes[$keys[0]] : null;
+		} else {
+			$values = [];
+			foreach ($keys as $name) {
+				$values[$name] = isset($this->_attributes[$name]) ? $this->_attributes[$name] : null;
+			}
+			return $values;
+		}
+	}
+
+	/**
+	 * Returns the old primary key value(s).
+	 * This refers to the primary key value that is populated into the record
+	 * after executing a find method (e.g. find(), findAll()).
+	 * The value remains unchanged even if the primary key attribute is manually assigned with a different value.
+	 * @param boolean $asArray whether to return the primary key value as an array. If true,
+	 * the return value will be an array with column name as key and column value as value.
+	 * If this is false (default), a scalar value will be returned for non-composite primary key.
+	 * @property mixed The old primary key value. An array (column name => column value) is
+	 * returned if the primary key is composite. A string is returned otherwise (null will be
+	 * returned if the key value is null).
+	 * @return mixed the old primary key value. An array (column name => column value) is returned if the primary key
+	 * is composite or `$asArray` is true. A string is returned otherwise (null will be returned if
+	 * the key value is null).
+	 */
+	public function getOldPrimaryKey($asArray = false)
+	{
+		$keys = $this->primaryKey();
+		if (count($keys) === 1 && !$asArray) {
+			return isset($this->_oldAttributes[$keys[0]]) ? $this->_oldAttributes[$keys[0]] : null;
+		} else {
+			$values = [];
+			foreach ($keys as $name) {
+				$values[$name] = isset($this->_oldAttributes[$name]) ? $this->_oldAttributes[$name] : null;
+			}
+			return $values;
+		}
+	}
+
+	/**
+	 * Creates an active record object using a row of data.
+	 * This method is called by [[ActiveQuery]] to populate the query results
+	 * into Active Records. It is not meant to be used to create new records.
+	 * @param array $row attribute values (name => value)
+	 * @return ActiveRecord the newly created active record.
+	 */
+	public static function create($row)
+	{
+		$record = static::instantiate($row);
+		$columns = array_flip($record->attributes());
+		foreach ($row as $name => $value) {
+			if (isset($columns[$name])) {
+				$record->_attributes[$name] = $value;
+			} else {
+				$record->$name = $value;
+			}
+		}
+		$record->_oldAttributes = $record->_attributes;
+		$record->afterFind();
+		return $record;
+	}
+
+	/**
+	 * Creates an active record instance.
+	 * This method is called by [[create()]].
+	 * You may override this method if the instance being created
+	 * depends on the row data to be populated into the record.
+	 * For example, by creating a record based on the value of a column,
+	 * you may implement the so-called single-table inheritance mapping.
+	 * @param array $row row data to be populated into the record.
+	 * @return ActiveRecord the newly created active record
+	 */
+	public static function instantiate($row)
+	{
+		return new static;
+	}
+
+	/**
+	 * Returns whether there is an element at the specified offset.
+	 * This method is required by the interface ArrayAccess.
+	 * @param mixed $offset the offset to check on
+	 * @return boolean whether there is an element at the specified offset.
+	 */
+	public function offsetExists($offset)
+	{
+		return $this->__isset($offset);
+	}
+
+	/**
+	 * Returns the relation object with the specified name.
+	 * A relation is defined by a getter method which returns an [[ActiveRelation]] object.
+	 * It can be declared in either the Active Record class itself or one of its behaviors.
+	 * @param string $name the relation name
+	 * @return ActiveRelation the relation object
+	 * @throws InvalidParamException if the named relation does not exist.
+	 */
+	public function getRelation($name)
+	{
+		$getter = 'get' . $name;
+		try {
+			$relation = $this->$getter();
+			if ($relation instanceof ActiveRelationInterface) {
+				return $relation;
+			} else {
+				throw new InvalidParamException(get_class($this) . ' has no relation named "' . $name . '".');
+			}
+		} catch (UnknownMethodException $e) {
+			throw new InvalidParamException(get_class($this) . ' has no relation named "' . $name . '".', 0, $e);
+		}
+	}
+
+	/**
+	 * Establishes the relationship between two models.
+	 *
+	 * The relationship is established by setting the foreign key value(s) in one model
+	 * to be the corresponding primary key value(s) in the other model.
+	 * The model with the foreign key will be saved into database without performing validation.
+	 *
+	 * If the relationship involves a pivot table, a new row will be inserted into the
+	 * pivot table which contains the primary key values from both models.
+	 *
+	 * Note that this method requires that the primary key value is not null.
+	 *
+	 * @param string $name the case sensitive name of the relationship
+	 * @param ActiveRecord $model the model to be linked with the current one.
+	 * @param array $extraColumns additional column values to be saved into the pivot table.
+	 * This parameter is only meaningful for a relationship involving a pivot table
+	 * (i.e., a relation set with `[[ActiveRelation::via()]]` or `[[ActiveRelation::viaTable()]]`.)
+	 * @throws InvalidCallException if the method is unable to link two models.
+	 */
+	public function link($name, $model, $extraColumns = [])
+	{
+		$relation = $this->getRelation($name);
+
+		if ($relation->via !== null) {
+			if ($this->getIsNewRecord() || $model->getIsNewRecord()) {
+				throw new InvalidCallException('Unable to link models: both models must NOT be newly created.');
+			}
+			if (is_array($relation->via)) {
+				/** @var ActiveRelation $viaRelation */
+				list($viaName, $viaRelation) = $relation->via;
+				$viaClass = $viaRelation->modelClass;
+				// unset $viaName so that it can be reloaded to reflect the change
+				unset($this->_related[$viaName]);
+			} else {
+				$viaRelation = $relation->via;
+				$viaTable = reset($relation->via->from);
+			}
+			$columns = [];
+			foreach ($viaRelation->link as $a => $b) {
+				$columns[$a] = $this->$b;
+			}
+			foreach ($relation->link as $a => $b) {
+				$columns[$b] = $model->$a;
+			}
+			foreach ($extraColumns as $k => $v) {
+				$columns[$k] = $v;
+			}
+			if (is_array($relation->via)) {
+				/** @var $viaClass ActiveRecord */
+				/** @var $record ActiveRecord */
+				$record = new $viaClass();
+				foreach($columns as $column => $value) {
+					$record->$column = $value;
+				}
+				$record->insert(false);
+			} else {
+				/** @var $viaTable string */
+				static::getDb()->createCommand()
+					->insert($viaTable, $columns)->execute();
+			}
+		} else {
+			$p1 = $model->isPrimaryKey(array_keys($relation->link));
+			$p2 = $this->isPrimaryKey(array_values($relation->link));
+			if ($p1 && $p2) {
+				if ($this->getIsNewRecord() && $model->getIsNewRecord()) {
+					throw new InvalidCallException('Unable to link models: both models are newly created.');
+				} elseif ($this->getIsNewRecord()) {
+					$this->bindModels(array_flip($relation->link), $this, $model);
+				} else {
+					$this->bindModels($relation->link, $model, $this);
+				}
+			} elseif ($p1) {
+				$this->bindModels(array_flip($relation->link), $this, $model);
+			} elseif ($p2) {
+				$this->bindModels($relation->link, $model, $this);
+			} else {
+				throw new InvalidCallException('Unable to link models: the link does not involve any primary key.');
+			}
+		}
+
+		// update lazily loaded related objects
+		if (!$relation->multiple) {
+			$this->_related[$name] = $model;
+		} elseif (isset($this->_related[$name])) {
+			if ($relation->indexBy !== null) {
+				$indexBy = $relation->indexBy;
+				$this->_related[$name][$model->$indexBy] = $model;
+			} else {
+				$this->_related[$name][] = $model;
+			}
+		}
+	}
+
+	/**
+	 * Destroys the relationship between two models.
+	 *
+	 * The model with the foreign key of the relationship will be deleted if `$delete` is true.
+	 * Otherwise, the foreign key will be set null and the model will be saved without validation.
+	 *
+	 * @param string $name the case sensitive name of the relationship.
+	 * @param ActiveRecord $model the model to be unlinked from the current one.
+	 * @param boolean $delete whether to delete the model that contains the foreign key.
+	 * If false, the model's foreign key will be set null and saved.
+	 * If true, the model containing the foreign key will be deleted.
+	 * @throws InvalidCallException if the models cannot be unlinked
+	 */
+	public function unlink($name, $model, $delete = false)
+	{
+		$relation = $this->getRelation($name);
+
+		if ($relation->via !== null) {
+			if (is_array($relation->via)) {
+				/** @var ActiveRelation $viaRelation */
+				list($viaName, $viaRelation) = $relation->via;
+				$viaClass = $viaRelation->modelClass;
+				unset($this->_related[$viaName]);
+			} else {
+				$viaRelation = $relation->via;
+				$viaTable = reset($relation->via->from);
+			}
+			$columns = [];
+			foreach ($viaRelation->link as $a => $b) {
+				$columns[$a] = $this->$b;
+			}
+			foreach ($relation->link as $a => $b) {
+				$columns[$b] = $model->$a;
+			}
+			if (is_array($relation->via)) {
+				/** @var $viaClass ActiveRecord */
+				if ($delete) {
+					$viaClass::deleteAll($columns);
+				} else {
+					$nulls = [];
+					foreach (array_keys($columns) as $a) {
+						$nulls[$a] = null;
+					}
+					$viaClass::updateAll($nulls, $columns);
+				}
+			} else {
+				/** @var $viaTable string */
+				$command = static::getDb()->createCommand();
+				if ($delete) {
+					$command->delete($viaTable, $columns)->execute();
+				} else {
+					$nulls = [];
+					foreach (array_keys($columns) as $a) {
+						$nulls[$a] = null;
+					}
+					$command->update($viaTable, $nulls, $columns)->execute();
+				}
+			}
+		} else {
+			$p1 = $model->isPrimaryKey(array_keys($relation->link));
+			$p2 = $this->isPrimaryKey(array_values($relation->link));
+			if ($p1 && $p2 || $p2) {
+				foreach ($relation->link as $a => $b) {
+					$model->$a = null;
+				}
+				$delete ? $model->delete() : $model->save(false);
+			} elseif ($p1) {
+				foreach ($relation->link as $b) {
+					$this->$b = null;
+				}
+				$delete ? $this->delete() : $this->save(false);
+			} else {
+				throw new InvalidCallException('Unable to unlink models: the link does not involve any primary key.');
+			}
+		}
+
+		if (!$relation->multiple) {
+			unset($this->_related[$name]);
+		} elseif (isset($this->_related[$name])) {
+			/** @var ActiveRecord $b */
+			foreach ($this->_related[$name] as $a => $b) {
+				if ($model->getPrimaryKey() == $b->getPrimaryKey()) {
+					unset($this->_related[$name][$a]);
+				}
+			}
+		}
+	}
+
+	/**
+	 * @param array $link
+	 * @param ActiveRecord $foreignModel
+	 * @param ActiveRecord $primaryModel
+	 * @throws InvalidCallException
+	 */
+	private function bindModels($link, $foreignModel, $primaryModel)
+	{
+		foreach ($link as $fk => $pk) {
+			$value = $primaryModel->$pk;
+			if ($value === null) {
+				throw new InvalidCallException('Unable to link models: the primary key of ' . get_class($primaryModel) . ' is null.');
+			}
+			$foreignModel->$fk = $value;
+		}
+		$foreignModel->save(false);
+	}
+
+	/**
+	 * Returns a value indicating whether the given set of attributes represents the primary key for this model
+	 * @param array $keys the set of attributes to check
+	 * @return boolean whether the given set of attributes represents the primary key for this model
+	 */
+	public static function isPrimaryKey($keys)
+	{
+		$pks = static::primaryKey();
+		foreach ($keys as $key) {
+			if (!in_array($key, $pks, true)) {
+				return false;
+			}
+		}
+		return count($keys) === count($pks);
+	}
+}
diff --git a/framework/yii/test/DbFixtureManager.php b/framework/yii/test/DbFixtureManager.php
index ed90284..23d25d4 100644
--- a/framework/yii/test/DbFixtureManager.php
+++ b/framework/yii/test/DbFixtureManager.php
@@ -11,6 +11,7 @@ use Yii;
 use yii\base\Component;
 use yii\base\InvalidConfigException;
 use yii\db\ActiveRecord;
+use yii\db\ActiveRecordInterface;
 use yii\db\Connection;
 
 /**
@@ -92,7 +93,7 @@ class DbFixtureManager extends Component
 		foreach ($fixtures as $name => $fixture) {
 			if (strpos($fixture, '\\') !== false) {
 				$model = new $fixture;
-				if ($model instanceof ActiveRecord) {
+				if ($model instanceof ActiveRecordInterface) {
 					$this->_modelClasses[$name] = $fixture;
 					$fixtures[$name] = $model->getTableSchema()->name;
 				} else {
diff --git a/framework/yii/validators/UniqueValidator.php b/framework/yii/validators/UniqueValidator.php
index 053f795..d123aad 100644
--- a/framework/yii/validators/UniqueValidator.php
+++ b/framework/yii/validators/UniqueValidator.php
@@ -10,6 +10,7 @@ namespace yii\validators;
 use Yii;
 use yii\base\InvalidConfigException;
 use yii\db\ActiveRecord;
+use yii\db\ActiveRecordInterface;
 
 /**
  * UniqueValidator validates that the attribute value is unique in the corresponding database table.
@@ -67,7 +68,7 @@ class UniqueValidator extends Validator
 		$query = $className::find();
 		$query->where([$attributeName => $value]);
 
-		if (!$object instanceof ActiveRecord || $object->getIsNewRecord()) {
+		if (!$object instanceof ActiveRecordInterface || $object->getIsNewRecord()) {
 			// if current $object isn't in the database yet then it's OK just to call exists()
 			$exists = $query->exists();
 		} else {