yii2/docs/guide/db-active-record.md

Active Record

Note: This section is under development.

Active Record provides an object-oriented interface for accessing data stored in a database. An Active Record class is associated with a database table, an Active Record instance corresponds to a row of that table, and an attribute of an Active Record instance represents the value of a column in that row. Instead of writing raw SQL statements, you can work with Active Record in an object-oriented fashion to manipulate the data in database tables.

For example, assume Customer is an Active Record class is associated with the customer table and name is a column of customer table. You can write the following code to insert a new row into customer table:

$customer = new Customer();
$customer->name = 'Qiang';
$customer->save();

The above code is equivalent to using the following raw SQL statement, which is less intuitive, more error prone, and may have compatibility problems for different DBMS:

$db->createCommand('INSERT INTO customer (name) VALUES (:name)', [
    ':name' => 'Qiang',
])->execute();

Below is the list of databases that are currently supported by Yii Active Record:

• MySQL 4.1 or later: via yii\db\ActiveRecord
• PostgreSQL 7.3 or later: via yii\db\ActiveRecord
• SQLite 2 and 3: via yii\db\ActiveRecord
• Microsoft SQL Server 2010 or later: via yii\db\ActiveRecord
• Oracle: via yii\db\ActiveRecord
• CUBRID 9.1 or later: via yii\db\ActiveRecord
• Sphnix: via yii\sphinx\ActiveRecord, requires yii2-sphinx extension
• ElasticSearch: via yii\elasticsearch\ActiveRecord, requires yii2-elasticsearch extension
• Redis 2.6.12 or later: via yii\redis\ActiveRecord, requires yii2-redis extension
• MongoDB 1.3.0 or later: via yii\mongodb\ActiveRecord, requires yii2-mongodb extension

As you can see, Yii provides Active Record support for relational databases as well as NoSQL databases. In this tutorial, we will mainly describe the usage of Active Record for relational databases. However, most content described here are also applicable to Active Record for NoSQL databases.

Declaring Active Record Classes

To declare an Active Record class you need to extend yii\db\ActiveRecord and implement the tableName method that returns the name of the database table associated with the class:

namespace app\models;

use yii\db\ActiveRecord;

class Customer extends ActiveRecord
{
    /**
     * @return string the name of the table associated with this ActiveRecord class.
     */
    public static function tableName()
    {
        return 'customer';
    }
}

Accessing Column Data

Active Record maps each column of the corresponding database table row to an attribute in the Active Record object. An attribute behaves like a regular object public property. The name of an attribute is the same as the corresponding column name and is case-sensitive.

To read the value of a column, you can use the following syntax:

// "id" and "email" are the names of columns in the table associated with $customer ActiveRecord object
$id = $customer->id;
$email = $customer->email;

To change the value of a column, assign a new value to the associated property and save the object:

$customer->email = 'jane@example.com';
$customer->save();

Connecting to Database

Active Record uses a yii\db\Connection to exchange data with database. By default, it uses the db application component as the connection. As explained in Database basics, you may configure the db component in the application configuration file like follows,

return [
    'components' => [
        'db' => [
            'class' => 'yii\db\Connection',
            'dsn' => 'mysql:host=localhost;dbname=testdb',
            'username' => 'demo',
            'password' => 'demo',
        ],
    ],
];

If you are using multiple databases in your application and you want to use a different DB connection for your Active Record class, you may override the yii\db\ActiveRecord::getDb() method:

class Customer extends ActiveRecord
{
    // ...

    public static function getDb()
    {
        return \Yii::$app->db2;  // use "db2" application component
    }
}

Querying Data from Database

Active Record provides two entry methods for building DB queries and populating data into Active Record instances:

• yii\db\ActiveRecord::find()
• yii\db\ActiveRecord::findBySql()

Both methods return an yii\db\ActiveQuery instance, which extends yii\db\Query, and thus supports the same set of flexible and powerful DB query building methods, such as where(), join(), orderBy(), etc. The following examples demonstrate some of the possibilities.

// to retrieve all *active* customers and order them by their ID:
$customers = Customer::find()
    ->where(['status' => Customer::STATUS_ACTIVE])
    ->orderBy('id')
    ->all();

// to return a single customer whose ID is 1:
$customer = Customer::find()
    ->where(['id' => 1])
    ->one();

// to return the number of *active* customers:
$count = Customer::find()
    ->where(['status' => Customer::STATUS_ACTIVE])
    ->count();

// to index the result by customer IDs:
$customers = Customer::find()->indexBy('id')->all();
// $customers array is indexed by customer IDs

// to retrieve customers using a raw SQL statement:
$sql = 'SELECT * FROM customer';
$customers = Customer::findBySql($sql)->all();

Tip: In the code above Customer::STATUS_ACTIVE is a constant defined in Customer. It is a good practice to use meaningful constant names rather than hardcoded strings or numbers in your code.

Two shortcut methods are provided to return Active Record instances matching a primary key value or a set of column values: findOne() and findAll(). The former returns the first matching instance while the latter returns all of them. For example,

// to return a single customer whose ID is 1:
$customer = Customer::findOne(1);

// to return an *active* customer whose ID is 1:
$customer = Customer::findOne([
    'id' => 1,
    'status' => Customer::STATUS_ACTIVE,
]);

// to return customers whose ID is 1, 2 or 3:
$customers = Customer::findAll([1, 2, 3]);

// to return customers whose status is "deleted":
$customer = Customer::findAll([
    'status' => Customer::STATUS_DELETED,
]);

Retrieving Data in Arrays

Sometimes when you are processing a large amount of data, you may want to use arrays to hold the data retrieved from database to save memory. This can be done by calling asArray():

// to return customers in terms of arrays rather than `Customer` objects:
$customers = Customer::find()
    ->asArray()
    ->all();
// each element of $customers is an array of name-value pairs

Note that while this method saves memory and improves performance it is a step to a lower abstraction layer and you will loose some features that the active record layer has. Fetching data using asArray is nearly equal to running a normal query using the query builder. When using asArray the result will be returned just as such a query and no typecasting is performed anymore so the result may contain string values for fields that are integer when accessed on the active record object.

Retrieving Data in Batches

In Query Builder, we have explained that you may use batch query to keep your memory usage under a limit when querying a large amount of data from database. You may use the same technique in Active Record. For example,

// fetch 10 customers at a time
foreach (Customer::find()->batch(10) as $customers) {
    // $customers is an array of 10 or fewer Customer objects
}
// fetch 10 customers at a time and iterate them one by one
foreach (Customer::find()->each(10) as $customer) {
    // $customer is a Customer object
}
// batch query with eager loading
foreach (Customer::find()->with('orders')->each() as $customer) {
}

Manipulating Data in Database

Active Record provides the following methods to insert, update and delete a single row in a table associated with a single Active Record instance:

• yii\db\ActiveRecord::save()
• yii\db\ActiveRecord::insert()
• yii\db\ActiveRecord::update()
• yii\db\ActiveRecord::delete()

Active Record also provides the following static methods that apply to a whole table associated with an Active Record class. Be extremely careful when using these methods as they affect the whole table. For example, deleteAll() will delete ALL rows in the table.

• yii\db\ActiveRecord::updateCounters()
• yii\db\ActiveRecord::updateAll()
• yii\db\ActiveRecord::updateAllCounters()
• yii\db\ActiveRecord::deleteAll()

The following examples show how to use these methods:

// to insert a new customer record
$customer = new Customer();
$customer->name = 'James';
$customer->email = 'james@example.com';
$customer->save();  // equivalent to $customer->insert();

// to update an existing customer record
$customer = Customer::findOne($id);
$customer->email = 'james@example.com';
$customer->save();  // equivalent to $customer->update();

// to delete an existing customer record
$customer = Customer::findOne($id);
$customer->delete();

// to delete several customers
Customer::deleteAll('age > :age AND gender = :gender', [':age' => 20, ':gender' => 'M']);

// to increment the age of ALL customers by 1
Customer::updateAllCounters(['age' => 1]);

Info: The save() method will call either insert() or update(), depending on whether the Active Record instance is new or not (internally it will check the value of yii\db\ActiveRecord::isNewRecord). If an Active Record is instantiated via the new operator, calling save() will insert a row in the table; calling save() on active record fetched from database will update the corresponding row in the table.

Data Input and Validation

Because Active Record extends from yii\base\Model, it supports the same data input and validation features as described in Model. For example, you may declare validation rules by overwriting the yii\base\Model::rules() method; you may massively assign user input data to an Active Record instance; and you may call yii\base\Model::validate() to trigger data validation.

When you call save(), insert() or update(), these methods will automatically call yii\base\Model::validate(). If the validation fails, the corresponding data saving operation will be cancelled.

The following example shows how to use an Active Record to collect/validate user input and save them into database:

// creating a new record
$model = new Customer;
if ($model->load(Yii::$app->request->post()) && $model->save()) {
    // the user input has been collected, validated and saved
}

// updating a record whose primary key is $id
$model = Customer::findOne($id);
if ($model === null) {
    throw new NotFoundHttpException;
}
if ($model->load(Yii::$app->request->post()) && $model->save()) {
    // the user input has been collected, validated and saved
}

Loading Default Values

Your table columns may be defined with default values. Sometimes, you may want to pre-populate your Web form for an Active Record with these values. To do so, call the loadDefaultValues() method before rendering the form:

$customer = new Customer();
$customer->loadDefaultValues();
// ... render HTML form for $customer ...

Active Record Life Cycles

It is important to understand the life cycles of Active Record when it is used to manipulate data in database. These life cycles are typically associated with corresponding events which allow you to inject code to intercept or respond to these events. They are especially useful for developing Active Record behaviors.

When instantiating a new Active Record instance, we will have the following life cycles:

1. constructor
2. yii\db\ActiveRecord::init(): will trigger an yii\db\ActiveRecord::EVENT_INIT event

When querying data through the yii\db\ActiveRecord::find() method, we will have the following life cycles for EVERY newly populated Active Record instance:

1. constructor
2. yii\db\ActiveRecord::init(): will trigger an yii\db\ActiveRecord::EVENT_INIT event
3. yii\db\ActiveRecord::afterFind(): will trigger an yii\db\ActiveRecord::EVENT_AFTER_FIND event

When calling yii\db\ActiveRecord::save() to insert or update an ActiveRecord, we will have the following life cycles:

1. yii\db\ActiveRecord::beforeValidate(): will trigger an yii\db\ActiveRecord::EVENT_BEFORE_VALIDATE event
2. yii\db\ActiveRecord::afterValidate(): will trigger an yii\db\ActiveRecord::EVENT_AFTER_VALIDATE event
3. yii\db\ActiveRecord::beforeSave(): will trigger an yii\db\ActiveRecord::EVENT_BEFORE_INSERT or yii\db\ActiveRecord::EVENT_BEFORE_UPDATE event
4. perform the actual data insertion or updating
5. yii\db\ActiveRecord::afterSave(): will trigger an yii\db\ActiveRecord::EVENT_AFTER_INSERT or yii\db\ActiveRecord::EVENT_AFTER_UPDATE event

And Finally when calling yii\db\ActiveRecord::delete() to delete an ActiveRecord, we will have the following life cycles:

1. yii\db\ActiveRecord::beforeDelete(): will trigger an yii\db\ActiveRecord::EVENT_BEFORE_DELETE event
2. perform the actual data deletion
3. yii\db\ActiveRecord::afterDelete(): will trigger an yii\db\ActiveRecord::EVENT_AFTER_DELETE event

Working with Relational Data

You can use ActiveRecord to also query a table's relational data (i.e., selection of data from Table A can also pull in related data from Table B). Thanks to ActiveRecord, the relational data returned can be accessed like a property of the ActiveRecord object associated with the primary table.

For example, with an appropriate relation declaration, by accessing $customer->orders you may obtain an array of Order objects which represent the orders placed by the specified customer.

To declare a relation, define a getter method which returns an yii\db\ActiveQuery object that has relation information about the relation context and thus will only query for related records. For example,

class Customer extends \yii\db\ActiveRecord
{
    public function getOrders()
    {
        // Customer has_many Order via Order.customer_id -> id
        return $this->hasMany(Order::className(), ['customer_id' => 'id']);
    }
}

class Order extends \yii\db\ActiveRecord
{
    public function getCustomer()
    {
        // Order has_one Customer via Customer.id -> customer_id
        return $this->hasOne(Customer::className(), ['id' => 'customer_id']);
    }
}

The methods yii\db\ActiveRecord::hasMany() and yii\db\ActiveRecord::hasOne() used in the above are used to model the many-one relationship and one-one relationship in a relational database. For example, a customer has many orders, and an order has one customer. Both methods take two parameters and return an yii\db\ActiveQuery object:

• $class: the name of the class of the related model(s). This should be a fully qualified class name.
• $link: the association between columns from the two tables. This should be given as an array. The keys of the array are the names of the columns from the table associated with $class, while the values of the array are the names of the columns from the declaring class. It is a good practice to define relationships based on table foreign keys.

After declaring relations, getting relational data is as easy as accessing a component property that is defined by the corresponding getter method:

// get the orders of a customer
$customer = Customer::findOne(1);
$orders = $customer->orders;  // $orders is an array of Order objects

Behind the scene, the above code executes the following two SQL queries, one for each line of code:

SELECT * FROM customer WHERE id=1;
SELECT * FROM order WHERE customer_id=1;

Tip: If you access the expression $customer->orders again, it will not perform the second SQL query again. The SQL query is only performed the first time when this expression is accessed. Any further accesses will only return the previously fetched results that are cached internally. If you want to re-query the relational data, simply unset the existing one first: unset($customer->orders);.

Sometimes, you may want to pass parameters to a relational query. For example, instead of returning all orders of a customer, you may want to return only big orders whose subtotal exceeds a specified amount. To do so, declare a bigOrders relation with the following getter method:

class Customer extends \yii\db\ActiveRecord
{
    public function getBigOrders($threshold = 100)
    {
        return $this->hasMany(Order::className(), ['customer_id' => 'id'])
            ->where('subtotal > :threshold', [':threshold' => $threshold])
            ->orderBy('id');
    }
}

Remember that hasMany() returns an yii\db\ActiveQuery object which allows you to customize the query by calling the methods of yii\db\ActiveQuery.

With the above declaration, if you access $customer->bigOrders, it will only return the orders whose subtotal is greater than 100. To specify a different threshold value, use the following code:

$orders = $customer->getBigOrders(200)->all();

Note: A relation method returns an instance of yii\db\ActiveQuery. If you access the relation like an attribute (i.e. a class property), the return value will be the query result of the relation, which could be an instance of yii\db\ActiveRecord, an array of that, or null, depending the multiplicity of the relation. For example, $customer->getOrders() returns an ActiveQuery instance, while $customer->orders returns an array of Order objects (or an empty array if the query results in nothing).

Relations with Pivot Table

Sometimes, two tables are related together via an intermediary table called pivot table. To declare such relations, we can customize the yii\db\ActiveQuery object by calling its yii\db\ActiveQuery::via() or yii\db\ActiveQuery::viaTable() method.

For example, if table order and table item are related via pivot table order_item, we can declare the items relation in the Order class like the following:

class Order extends \yii\db\ActiveRecord
{
    public function getItems()
    {
        return $this->hasMany(Item::className(), ['id' => 'item_id'])
            ->viaTable('order_item', ['order_id' => 'id']);
    }
}

The yii\db\ActiveQuery::via() method is similar to yii\db\ActiveQuery::viaTable() except that the first parameter of yii\db\ActiveQuery::via() takes a relation name declared in the ActiveRecord class instead of the pivot table name. For example, the above items relation can be equivalently declared as follows:

class Order extends \yii\db\ActiveRecord
{
    public function getOrderItems()
    {
        return $this->hasMany(OrderItem::className(), ['order_id' => 'id']);
    }

    public function getItems()
    {
        return $this->hasMany(Item::className(), ['id' => 'item_id'])
            ->via('orderItems');
    }
}

Lazy and Eager Loading

As described earlier, when you access the related objects the first time, ActiveRecord will perform a DB query to retrieve the corresponding data and populate it into the related objects. No query will be performed if you access the same related objects again. We call this lazy loading. For example,

// SQL executed: SELECT * FROM customer WHERE id=1
$customer = Customer::findOne(1);
// SQL executed: SELECT * FROM order WHERE customer_id=1
$orders = $customer->orders;
// no SQL executed
$orders2 = $customer->orders;

Lazy loading is very convenient to use. However, it may suffer from a performance issue in the following scenario:

// SQL executed: SELECT * FROM customer LIMIT 100
$customers = Customer::find()->limit(100)->all();

foreach ($customers as $customer) {
    // SQL executed: SELECT * FROM order WHERE customer_id=...
    $orders = $customer->orders;
    // ...handle $orders...
}

How many SQL queries will be performed in the above code, assuming there are more than 100 customers in the database? 101! The first SQL query brings back 100 customers. Then for each customer, a SQL query is performed to bring back the orders of that customer.

To solve the above performance problem, you can use the so-called eager loading approach by calling yii\db\ActiveQuery::with():

// SQL executed: SELECT * FROM customer LIMIT 100;
//               SELECT * FROM orders WHERE customer_id IN (1,2,...)
$customers = Customer::find()->limit(100)
    ->with('orders')->all();

foreach ($customers as $customer) {
    // no SQL executed
    $orders = $customer->orders;
    // ...handle $orders...
}

As you can see, only two SQL queries are needed for the same task!

Info: In general, if you are eager loading N relations among which M relations are defined with via() or viaTable(), a total number of 1+M+N SQL queries will be performed: one query to bring back the rows for the primary table, one for each of the M pivot tables corresponding to the via() or viaTable() calls, and one for each of the N related tables.

Note: When you are customizing select() with eager loading, make sure you include the columns that link the related models. Otherwise, the related models will not be loaded. For example,

$orders = Order::find()->select(['id', 'amount'])->with('customer')->all();
// $orders[0]->customer is always null. To fix the problem, you should do the following:
$orders = Order::find()->select(['id', 'amount', 'customer_id'])->with('customer')->all();

Sometimes, you may want to customize the relational queries on the fly. This can be done for both lazy loading and eager loading. For example,

$customer = Customer::findOne(1);
// lazy loading: SELECT * FROM order WHERE customer_id=1 AND subtotal>100
$orders = $customer->getOrders()->where('subtotal>100')->all();

// eager loading: SELECT * FROM customer LIMIT 100
//                SELECT * FROM order WHERE customer_id IN (1,2,...) AND subtotal>100
$customers = Customer::find()->limit(100)->with([
    'orders' => function($query) {
        $query->andWhere('subtotal>100');
    },
])->all();

Inverse Relations

Relations can often be defined in pairs. For example, Customer may have a relation named orders while Order may have a relation named customer:

class Customer extends ActiveRecord
{
    ....
    public function getOrders()
    {
        return $this->hasMany(Order::className(), ['customer_id' => 'id']);
    }
}

class Order extends ActiveRecord
{
    ....
    public function getCustomer()
    {
        return $this->hasOne(Customer::className(), ['id' => 'customer_id']);
    }
}

If we perform the following query, we would find that the customer of an order is not the same customer object that finds those orders, and accessing customer->orders will trigger one SQL execution while accessing the customer of an order will trigger another SQL execution:

// SELECT * FROM customer WHERE id=1
$customer = Customer::findOne(1);
// echoes "not equal"
// SELECT * FROM order WHERE customer_id=1
// SELECT * FROM customer WHERE id=1
if ($customer->orders[0]->customer === $customer) {
    echo 'equal';
} else {
    echo 'not equal';
}

To avoid the redundant execution of the last SQL statement, we could declare the inverse relations for the customer and the orders relations by calling the yii\db\ActiveQuery::inverseOf() method, like the following:

class Customer extends ActiveRecord
{
    ....
    public function getOrders()
    {
        return $this->hasMany(Order::className(), ['customer_id' => 'id'])->inverseOf('customer');
    }
}

Now if we execute the same query as shown above, we would get:

// SELECT * FROM customer WHERE id=1
$customer = Customer::findOne(1);
// echoes "equal"
// SELECT * FROM order WHERE customer_id=1
if ($customer->orders[0]->customer === $customer) {
    echo 'equal';
} else {
    echo 'not equal';
}

In the above, we have shown how to use inverse relations in lazy loading. Inverse relations also apply in eager loading:

// SELECT * FROM customer
// SELECT * FROM order WHERE customer_id IN (1, 2, ...)
$customers = Customer::find()->with('orders')->all();
// echoes "equal"
if ($customers[0]->orders[0]->customer === $customers[0]) {
    echo 'equal';
} else {
    echo 'not equal';
}

Note: Inverse relation cannot be defined with a relation that involves pivoting tables. That is, if your relation is defined with yii\db\ActiveQuery::via() or yii\db\ActiveQuery::viaTable(), you cannot call yii\db\ActiveQuery::inverseOf() further.

Joining with Relations

When working with relational databases, a common task is to join multiple tables and apply various query conditions and parameters to the JOIN SQL statement. Instead of calling yii\db\ActiveQuery::join() explicitly to build up the JOIN query, you may reuse the existing relation definitions and call yii\db\ActiveQuery::joinWith() to achieve this goal. For example,

// find all orders and sort the orders by the customer id and the order id. also eager loading "customer"
$orders = Order::find()->joinWith('customer')->orderBy('customer.id, order.id')->all();
// find all orders that contain books, and eager loading "books"
$orders = Order::find()->innerJoinWith('books')->all();

In the above, the method yii\db\ActiveQuery::innerJoinWith() is a shortcut to yii\db\ActiveQuery::joinWith() with the join type set as INNER JOIN.

You may join with one or multiple relations; you may apply query conditions to the relations on-the-fly; and you may also join with sub-relations. For example,

// join with multiple relations
// find out the orders that contain books and are placed by customers who registered within the past 24 hours
$orders = Order::find()->innerJoinWith([
    'books',
    'customer' => function ($query) {
        $query->where('customer.created_at > ' . (time() - 24 * 3600));
    }
])->all();
// join with sub-relations: join with books and books' authors
$orders = Order::find()->joinWith('books.author')->all();

Behind the scene, Yii will first execute a JOIN SQL statement to bring back the primary models satisfying the conditions applied to the JOIN SQL. It will then execute a query for each relation and populate the corresponding related records.

The difference between yii\db\ActiveQuery::joinWith() and yii\db\ActiveQuery::with() is that the former joins the tables for the primary model class and the related model classes to retrieve the primary models, while the latter just queries against the table for the primary model class to retrieve the primary models.

Because of this difference, you may apply query conditions that are only available to a JOIN SQL statement. For example, you may filter the primary models by the conditions on the related models, like the example above. You may also sort the primary models using columns from the related tables.

When using yii\db\ActiveQuery::joinWith(), you are responsible to disambiguate column names. In the above examples, we use item.id and order.id to disambiguate the id column references because both of the order table and the item table contain a column named id.

By default, when you join with a relation, the relation will also be eagerly loaded. You may change this behavior by passing the $eagerLoading parameter which specifies whether to eager load the specified relations.

And also by default, yii\db\ActiveQuery::joinWith() uses LEFT JOIN to join the related tables. You may pass it with the $joinType parameter to customize the join type. As a shortcut to the INNER JOIN type, you may use yii\db\ActiveQuery::innerJoinWith().

Below are some more examples,

// find all orders that contain books, but do not eager loading "books".
$orders = Order::find()->innerJoinWith('books', false)->all();
// which is equivalent to the above
$orders = Order::find()->joinWith('books', false, 'INNER JOIN')->all();

Sometimes when joining two tables, you may need to specify some extra condition in the ON part of the JOIN query. This can be done by calling the yii\db\ActiveQuery::onCondition() method like the following:

class User extends ActiveRecord
{
    public function getBooks()
    {
        return $this->hasMany(Item::className(), ['owner_id' => 'id'])->onCondition(['category_id' => 1]);
    }
}

In the above, the yii\db\ActiveRecord::hasMany() method returns an yii\db\ActiveQuery instance, upon which yii\db\ActiveQuery::onCondition() is called to specify that only items whose category_id is 1 should be returned.

When you perform query using yii\db\ActiveQuery::joinWith(), the on-condition will be put in the ON part of the corresponding JOIN query. For example,

// SELECT user.* FROM user LEFT JOIN item ON item.owner_id=user.id AND category_id=1
// SELECT * FROM item WHERE owner_id IN (...) AND category_id=1
$users = User::find()->joinWith('books')->all();

Note that if you use eager loading via yii\db\ActiveQuery::with() or lazy loading, the on-condition will be put in the WHERE part of the corresponding SQL statement, because there is no JOIN query involved. For example,

// SELECT * FROM user WHERE id=10
$user = User::findOne(10);
// SELECT * FROM item WHERE owner_id=10 AND category_id=1
$books = $user->books;

Working with Relationships

ActiveRecord provides the following two methods for establishing and breaking a relationship between two ActiveRecord objects:

• yii\db\ActiveRecord::link()
• yii\db\ActiveRecord::unlink()

For example, given a customer and a new order, we can use the following code to make the order owned by the customer:

$customer = Customer::findOne(1);
$order = new Order();
$order->subtotal = 100;
$customer->link('orders', $order);

The yii\db\ActiveRecord::link() call above will set the customer_id of the order to be the primary key value of $customer and then call yii\db\ActiveRecord::save() to save the order into database.

Cross-DBMS Relations

ActiveRecord allows to establish relationship between entities from different DBMS. For example: between relational database table and MongoDB collection. Such relation does not require any special code:

// Relational database Active Record
class Customer extends \yii\db\ActiveRecord
{
    public static function tableName()
    {
        return 'customer';
    }

    public function getComments()
    {
        // Customer, stored in relational database, has many Comments, stored in MongoDB collection:
        return $this->hasMany(Comment::className(), ['customer_id' => 'id']);
    }
}

// MongoDb Active Record
class Comment extends \yii\mongodb\ActiveRecord
{
    public static function collectionName()
    {
        return 'comment';
    }

    public function getCustomer()
    {
        // Comment, stored in MongoDB collection, has one Customer, stored in relational database:
        return $this->hasOne(Customer::className(), ['id' => 'customer_id']);
    }
}

All Active Record features like eager and lazy loading, establishing and breaking a relationship and so on, are available for cross-DBMS relations.

Note: do not forget Active Record solutions for different DBMS may have specific methods and features, which may not be applied for cross-DBMS relations. For example: usage of yii\db\ActiveQuery::joinWith() will obviously not work with relation to the MongoDB collection.

Scopes

When you call yii\db\ActiveRecord::find() or yii\db\ActiveRecord::findBySql(), it returns an yii\db\ActiveQuery instance. You may call additional query methods, such as yii\db\ActiveQuery::where(), yii\db\ActiveQuery::orderBy(), to further specify the query conditions.

It is possible that you may want to call the same set of query methods in different places. If this is the case, you should consider defining the so-called scopes. A scope is essentially a method defined in a custom query class that calls a set of query methods to modify the query object. You can then use a scope like calling a normal query method.

Two steps are required to define a scope. First create a custom query class for your model and define the needed scope methods in this class. For example, create a CommentQuery class for the Comment model and define the active() scope method like the following:

namespace app\models;

use yii\db\ActiveQuery;

class CommentQuery extends ActiveQuery
{
    public function active($state = true)
    {
        $this->andWhere(['active' => $state]);
        return $this;
    }
}

Important points are:

1. Class should extend from yii\db\ActiveQuery (or another ActiveQuery such as yii\mongodb\ActiveQuery).
2. A method should be public and should return $this in order to allow method chaining. It may accept parameters.
3. Check yii\db\ActiveQuery methods that are very useful for modifying query conditions.

Second, override yii\db\ActiveRecord::find() to use the custom query class instead of the regular yii\db\ActiveQuery. For the example above, you need to write the following code:

namespace app\models;

use yii\db\ActiveRecord;

class Comment extends ActiveRecord
{
    /**
     * @inheritdoc
     * @return CommentQuery
     */
    public static function find()
    {
        return new CommentQuery(get_called_class());
    }
}

That's it. Now you can use your custom scope methods:

$comments = Comment::find()->active()->all();
$inactiveComments = Comment::find()->active(false)->all();

You can also use scopes when defining relations. For example,

class Post extends \yii\db\ActiveRecord
{
    public function getActiveComments()
    {
        return $this->hasMany(Comment::className(), ['post_id' => 'id'])->active();

    }
}

Or use the scopes on-the-fly when performing relational query:

$posts = Post::find()->with([
    'comments' => function($q) {
        $q->active();
    }
])->all();

Default Scope

If you used Yii 1.1 before, you may know a concept called default scope. A default scope is a scope that applies to ALL queries. You can define a default scope easily by overriding yii\db\ActiveRecord::find(). For example,

public static function find()
{
    return parent::find()->where(['deleted' => false]);
}

Note that all your queries should then not use yii\db\ActiveQuery::where() but yii\db\ActiveQuery::andWhere() and yii\db\ActiveQuery::orWhere() to not override the default condition.

Transactional operations

There are two ways of dealing with transactions while working with Active Record. First way is doing everything manually as described in "transactions" section of "Database basics". Another way is to do it by implementing transactions method where you can specify which operations are to be wrapped into transaction per model scenario:

class Post extends \yii\db\ActiveRecord
{
    return [
        'admin' => self::OP_INSERT,
        'api' => self::OP_INSERT | self::OP_UPDATE | self::OP_DELETE,
        // the above is equivalent to the following:
        // 'api' => self::OP_ALL,
    ];

In the above admin and api are model scenarios and constants starting with OP_ are operations that should be wrapped in transaction for these sceanarios. Supported operations are OP_INSERT, OP_UPDATE and OP_DELETE. OP_ALL stands for all three.

Such automatic transactions are especially useful if you're doing additional database changes in beforeSave, afterSave, beforeDelete, afterDelete and want to be sure that both succeeded before they are saved.

Optimistic Locks

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 \yii\db\StaleObjectException exception will be thrown, and the update or deletion is skipped.

Optimistic locking is only supported by update() and delete() methods and isn't used by default.

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 optimisticLock() 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 \yii\db\StaleObjectException and implement necessary business logic (e.g. merging the changes, prompting stated data) to resolve the conflict.

Dirty Attributes

An attribute is considered dirty if its value was modified since model was loaded from database or since most recent data save. When saving record data by calling save(), update(), insert() etc. only dirty attributes are saved into database. If there are no dirty attributes there's nothing to be saved so no query will be issued at all.

See also

• Model
• yii\db\ActiveRecord