diff --git a/framework/caching/ChainedDependency.php b/framework/caching/ChainedDependency.php
index 9c4e547..af34e9d 100644
--- a/framework/caching/ChainedDependency.php
+++ b/framework/caching/ChainedDependency.php
@@ -57,7 +57,7 @@ class ChainedDependency extends Dependency
 			if (!$dependency instanceof Dependency) {
 				$dependency = \Yii::createObject($dependency);
 			}
-			$dependency->evalulateDependency();
+			$dependency->evaluateDependency();
 		}
 	}
 
diff --git a/framework/caching/DbDependency.php b/framework/caching/DbDependency.php
index cbe0ae1..4308dc1 100644
--- a/framework/caching/DbDependency.php
+++ b/framework/caching/DbDependency.php
@@ -28,25 +28,23 @@ class DbDependency extends Dependency
 	public $db = 'db';
 	/**
 	 * @var string the SQL query whose result is used to determine if the dependency has been changed.
-	 * Only the first row of the query result will be used.
+	 * Only the first row of the query result will be used. This property must be always set, otherwise
+	 * an exception would be raised.
 	 */
 	public $sql;
 	/**
 	 * @var array the parameters (name=>value) to be bound to the SQL statement specified by [[sql]].
 	 */
-	public $params;
+	public $params = array();
 
 	/**
-	 * Constructor.
-	 * @param string $sql the SQL query whose result is used to determine if the dependency has been changed.
-	 * @param array $params the parameters (name=>value) to be bound to the SQL statement specified by [[sql]].
-	 * @param array $config name-value pairs that will be used to initialize the object properties
+	 * Initializes the database dependency object.
 	 */
-	public function __construct($sql, $params = array(), $config = array())
+	public function init()
 	{
-		$this->sql = $sql;
-		$this->params = $params;
-		parent::__construct($config);
+		if ($this->sql === null) {
+			throw new InvalidConfigException('DbDependency::sql must be set.');
+		}
 	}
 
 	/**
diff --git a/framework/caching/ExpressionDependency.php b/framework/caching/ExpressionDependency.php
index e13c962..bf70291 100644
--- a/framework/caching/ExpressionDependency.php
+++ b/framework/caching/ExpressionDependency.php
@@ -22,18 +22,7 @@ class ExpressionDependency extends Dependency
 	/**
 	 * @var string the PHP expression whose result is used to determine the dependency.
 	 */
-	public $expression;
-
-	/**
-	 * Constructor.
-	 * @param string $expression the PHP expression whose result is used to determine the dependency.
-	 * @param array $config name-value pairs that will be used to initialize the object properties
-	 */
-	public function __construct($expression = 'true', $config = array())
-	{
-		$this->expression = $expression;
-		parent::__construct($config);
-	}
+	public $expression = 'true';
 
 	/**
 	 * Generates the data needed to determine if dependency has been changed.
diff --git a/framework/caching/FileDependency.php b/framework/caching/FileDependency.php
index 3797dde..8d858ec 100644
--- a/framework/caching/FileDependency.php
+++ b/framework/caching/FileDependency.php
@@ -7,6 +7,8 @@
 
 namespace yii\caching;
 
+use yii\base\InvalidConfigException;
+
 /**
  * FileDependency represents a dependency based on a file's last modification time.
  *
@@ -20,19 +22,19 @@ class FileDependency extends Dependency
 {
 	/**
 	 * @var string the name of the file whose last modification time is used to
-	 * check if the dependency has been changed.
+	 * check if the dependency has been changed. This property must be always set,
+	 * otherwise an exception would be raised.
 	 */
 	public $fileName;
 
 	/**
-	 * Constructor.
-	 * @param string $fileName name of the file whose change is to be checked.
-	 * @param array $config name-value pairs that will be used to initialize the object properties
+	 * Initializes the database dependency object.
 	 */
-	public function __construct($fileName = null, $config = array())
+	public function init()
 	{
-		$this->fileName = $fileName;
-		parent::__construct($config);
+		if ($this->file === null) {
+			throw new InvalidConfigException('FileDependency::fileName must be set.');
+		}
 	}
 
 	/**
diff --git a/framework/widgets/FragmentCache.php b/framework/widgets/FragmentCache.php
index dae538a..637d115 100644
--- a/framework/widgets/FragmentCache.php
+++ b/framework/widgets/FragmentCache.php
@@ -8,7 +8,6 @@
 namespace yii\widgets;
 
 use Yii;
-use yii\base\InvalidConfigException;
 use yii\base\Widget;
 use yii\caching\Cache;
 use yii\caching\Dependency;