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Behaviors

Model behaviors are a way to organize some of the functionality defined in CakePHP models. They allow us to separate and reuse logic that creates a type of behavior, and they do this without requiring inheritance. For example creating tree structures. By providing a simple yet powerful way to enhance models, behaviors allow us to attach functionality to models by defining a simple class variable. That’s how behaviors allow models to get rid of all the extra weight that might not be part of the business contract they are modeling, or that is also needed in different models and can then be extrapolated.

As an example, consider a model that gives us access to a database table which stores structural information about a tree. Removing, adding, and migrating nodes in the tree is not as simple as deleting, inserting, and editing rows in the table. Many records may need to be updated as things move around. Rather than creating those tree-manipulation methods on a per model basis (for every model that needs that functionality), we could simply tell our model to use the TreeBehavior, or in more formal terms, we tell our model to behave as a Tree. This is known as attaching a behavior to a model. With just one line of code, our CakePHP model takes on a whole new set of methods that allow it to interact with the underlying structure.

CakePHP already includes behaviors for tree structures, translated content, access control list interaction, not to mention the community-contributed behaviors already available in the CakePHP Bakery (http://bakery.cakephp.org). In this section, we’ll cover the basic usage pattern for adding behaviors to models, how to use CakePHP’s built-in behaviors, and how to create our own.

In essence, Behaviors are Mixins with callbacks.

There are a number of Behaviors included in CakePHP. To find out more about each one, reference the chapters below:

Using Behaviors

Behaviors are attached to models through the $actsAs model class variable:

class Category extends AppModel {
    public $actsAs = array('Tree');
}

This example shows how a Category model could be managed in a tree structure using the TreeBehavior. Once a behavior has been specified, use the methods added by the behavior as if they always existed as part of the original model:

// Set ID
$this->Category->id = 42;

// Use behavior method, children():
$kids = $this->Category->children();

Some behaviors may require or allow settings to be defined when the behavior is attached to the model. Here, we tell our TreeBehavior the names of the “left” and “right” fields in the underlying database table:

class Category extends AppModel {
    public $actsAs = array('Tree' => array(
        'left'  => 'left_node',
        'right' => 'right_node'
    ));
}

We can also attach several behaviors to a model. There’s no reason why, for example, our Category model should only behave as a tree, it may also need internationalization support:

class Category extends AppModel {
    public $actsAs = array(
        'Tree' => array(
          'left'  => 'left_node',
          'right' => 'right_node'
        ),
        'Translate'
    );
}

So far we have been adding behaviors to models using a model class variable. That means that our behaviors will be attached to our models throughout the model’s lifetime. However, we may need to “detach” behaviors from our models at runtime. Let’s say that on our previous Category model, which is acting as a Tree and a Translate model, we need for some reason to force it to stop acting as a Translate model:

// Detach a behavior from our model:
$this->Category->Behaviors->unload('Translate');

That will make our Category model stop behaving as a Translate model from thereon. We may need, instead, to just disable the Translate behavior from acting upon our normal model operations: our finds, our saves, etc. In fact, we are looking to disable the behavior from acting upon our CakePHP model callbacks. Instead of detaching the behavior, we then tell our model to stop informing of these callbacks to the Translate behavior:

// Stop letting the behavior handle our model callbacks
$this->Category->Behaviors->disable('Translate');

We may also need to find out if our behavior is handling those model callbacks, and if not we then restore its ability to react to them:

// If our behavior is not handling model callbacks
if (!$this->Category->Behaviors->enabled('Translate')) {
    // Tell it to start doing so
    $this->Category->Behaviors->enable('Translate');
}

Just as we could completely detach a behavior from a model at runtime, we can also attach new behaviors. Say that our familiar Category model needs to start behaving as a Christmas model, but only on Christmas day:

// If today is Dec 25
if (date('m/d') === '12/25') {
    // Our model needs to behave as a Christmas model
    $this->Category->Behaviors->load('Christmas');
}

We can also use the load method to override behavior settings:

// We will change one setting from our already attached behavior
$this->Category->Behaviors->load('Tree', array('left' => 'new_left_node'));

There’s also a method to obtain the list of behaviors a model has attached. If we pass the name of a behavior to the method, it will tell us if that behavior is attached to the model, otherwise it will give us the list of attached behaviors:

// If the Translate behavior is not attached
if (!$this->Category->Behaviors->loaded('Translate')) {
    // Get the list of all behaviors the model has attached
    $behaviors = $this->Category->Behaviors->loaded();
}

Creating Behaviors

Behaviors that are attached to Models get their callbacks called automatically. The callbacks are similar to those found in Models: beforeFind, afterFind, beforeValidate, afterValidate, beforeSave, afterSave, beforeDelete, afterDelete and onError - see Callback Methods.

Your behaviors should be placed in app/Model/Behavior. They are named in CamelCase and postfixed by Behavior, ex. NameBehavior.php. It’s often helpful to use a core behavior as a template when creating your own. Find them in lib/Cake/Model/Behavior/.

Every callback and behavior method takes a reference to the model it is being called from as the first parameter.

Besides implementing the callbacks, you can add settings per behavior and/or model behavior attachment. Information about specifying settings can be found in the chapters about core behaviors and their configuration.

A quick example that illustrates how behavior settings can be passed from the model to the behavior:

class Post extends AppModel {
    public $actsAs = array(
        'YourBehavior' => array(
            'option1_key' => 'option1_value'
        )
    );
}

Since behaviors are shared across all the model instances that use them, it’s a good practice to store the settings per alias/model name that is using the behavior. When created behaviors will have their setup() method called:

public function setup(Model $Model, $settings = array()) {
    if (!isset($this->settings[$Model->alias])) {
        $this->settings[$Model->alias] = array(
            'option1_key' => 'option1_default_value',
            'option2_key' => 'option2_default_value',
            'option3_key' => 'option3_default_value',
        );
    }
    $this->settings[$Model->alias] = array_merge(
        $this->settings[$Model->alias], (array)$settings);
}

Creating behavior methods

Behavior methods are automatically available on any model acting as the behavior. For example if you had:

class Duck extends AppModel {
    public $actsAs = array('Flying');
}

You would be able to call FlyingBehavior methods as if they were methods on your Duck model. When creating behavior methods you automatically get passed a reference of the calling model as the first parameter. All other supplied parameters are shifted one place to the right. For example:

$this->Duck->fly('toronto', 'montreal');

Although this method takes two parameters, the method signature should look like:

public function fly(Model $Model, $from, $to) {
    // Do some flying.
}

Keep in mind that methods called in a $this->doIt() fashion from inside a behavior method will not get the $model parameter automatically appended.

Mapped methods

In addition to providing ‘mixin’ methods, behaviors can also provide pattern matching methods. Behaviors can also define mapped methods. Mapped methods use pattern matching for method invocation. This allows you to create methods similar to Model::findAllByXXX methods on your behaviors. Mapped methods need to be declared in your behaviors $mapMethods array. The method signature for a mapped method is slightly different than a normal behavior mixin method:

class MyBehavior extends ModelBehavior {
    public $mapMethods = array('/do(\w+)/' => 'doSomething');

    public function doSomething(Model $model, $method, $arg1, $arg2) {
        debug(func_get_args());
        //do something
    }
}

The above will map every doXXX() method call to the behavior. As you can see, the model is still the first parameter, but the called method name will be the 2nd parameter. This allows you to munge the method name for additional information, much like Model::findAllByXX. If the above behavior was attached to a model the following would happen:

$model->doReleaseTheHounds('homer', 'lenny');

// would output
'ReleaseTheHounds', 'homer', 'lenny'

Behavior callbacks

Model Behaviors can define a number of callbacks that are triggered before the model callbacks of the same name. Behavior callbacks allow your behaviors to capture events in attached models and augment the parameters or splice in additional behavior.

All behavior callbacks are fired before the model callbacks are:

  • beforeFind
  • afterFind
  • beforeValidate
  • afterValidate
  • beforeSave
  • afterSave
  • beforeDelete
  • afterDelete

Creating a behavior callback

class ModelBehavior

Model behavior callbacks are defined as simple methods in your behavior class. Much like regular behavior methods, they receive a $Model parameter as the first argument. This parameter is the model that the behavior method was invoked on.

ModelBehavior::setup(Model $Model, array $settings = array())

Called when a behavior is attached to a model. The settings come from the attached model’s $actsAs property.

ModelBehavior::cleanup(Model $Model)

Called when a behavior is detached from a model. The base method removes model settings based on $model->alias. You can override this method and provide custom cleanup functionality.

ModelBehavior::beforeFind(Model $Model, array $query)

If a behavior’s beforeFind return’s false it will abort the find(). Returning an array will augment the query parameters used for the find operation.

ModelBehavior::afterFind(Model $Model, mixed $results, boolean $primary = false)

You can use the afterFind to augment the results of a find. The return value will be passed on as the results to either the next behavior in the chain or the model’s afterFind.

ModelBehavior::beforeValidate(Model $Model, array $options = array())

You can use beforeValidate to modify a model’s validate array or handle any other pre-validation logic. Returning false from a beforeValidate callback will abort the validation and cause it to fail.

ModelBehavior::afterValidate(Model $Model)

You can use afterValidate to perform any data cleanup or preparation if needed.

ModelBehavior::beforeSave(Model $Model, array $options = array())

You can return false from a behavior’s beforeSave to abort the save. Return true to allow it continue.

ModelBehavior::afterSave(Model $Model, boolean $created, array $options = array())

You can use afterSave to perform clean up operations related to your behavior. $created will be true when a record is created, and false when a record is updated.

ModelBehavior::beforeDelete(Model $Model, boolean $cascade = true)

You can return false from a behavior’s beforeDelete to abort the delete. Return true to allow it continue.

ModelBehavior::afterDelete(Model $Model)

You can use afterDelete to perform clean up operations related to your behavior.