what is yii filter

Filter

A filter is an object that is executed before or after a controller action is executed. For example, an access control filter can control whether a specific end user has permission to perform an action before the action is executed, and a content compression filter can compress the response content after the action is executed before sending it to the end user. (Recommended learning: YII framework )

filter can contain pre -filtering (filter logic before action) or post -filtering (filtering logic after action), or at the same time includes two.

Using filters

Filters are essentially a special type of behavior, so using filters is the same as using behavior. You can declare filters by overriding its behaviors() method in the controller class, as shown below:

public function behaviors()
{
    return [
        [
            'class' => 'yii\filters\HttpCache',
            'only' => ['index', 'view'],
            'lastModified' => function ($action, $params) {
                $q = new \yii\db\Query();
                return $q->from('user')->max('updated_at');
            },
        ],
    ];
}

The filters of the controller class are applied to all actions of the class by default. You can configure the only attribute explicitly. Specify which actions the controller applies to. In the above example, the HttpCache filter only applies to the index and view actions. You can also configure the except attribute to prevent some actions from executing filters.

In addition to controllers, filters can be declared in modules or application bodies. After declaration, the filter will be applied to all controller actions belonging to the module or application body, unless the filter's only and except attributes are configured as above.

Note: When declaring filters in the module or application body, use routes instead of action IDs in the only and except attributes, because only the action ID cannot uniquely specify a specific action in the module or application body.

When an action has multiple filters, they are executed sequentially according to the following rules:

Pre-filtering

In order Execute the filters listed in behaviors() in the application body.

Execute the filters listed in behaviors() in the module in order.

Execute the filters listed in behaviors() in the controller in sequence.

If any filter terminates action execution, subsequent filters (including pre-filtering and post-filtering) will no longer be executed.

Execute the action after successfully passing pre-filtering.

Post-filtering

Execute the filters listed in behaviors() in the controller in reverse order.

Execute the filters listed in behaviors() in the module in reverse order.

Execute the filters listed in behaviors() in the application body in reverse order.

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