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Components

Components are used to aid controllers in specific situations. Rather than extend Cake’s core libraries, special functionality can be made into components.

A guy named olle on the IRC channel once said: A component is a sharable little “controllerette”. We find that this is a good definition. The main goal in fact is: reusability. Components are to controllers what helpers are to views. The main difference is that components encapsulate business logic whereas helpers encapsulate presentation logic. This point actually is very important, a common source of confusion for new Bakers when trying to achieve reusability: I’m trying to do X, should this be a component or a helper?! Well, the answer is really simple, what does X do? Does it do business logic or presentation logic, perhaps both? If it’s business logic then it’s a component. If it’s presentation logic then it’s a helper. If it’s both, then..well it’s both a component and a helper. An example of the later case would be an authentication system. You would want to login, logout, restrict access, and test permissions of a user to a resource (an action: add, edit, delete, or a url), this is business logic, so this authentication system should be a component. But you also want to add some entries to the main menu when the user is logged in, and this is presentation logic.

Creating your own

To create a component, add a file in app/controllers/components/ directory.

Let us assume you created foo.php. Inside of the file you need to define a class that corresponds to the file name (appending the word ‘Component’ to the file name). So in our case you would create the following contents:

A simple component

<?php
class FooComponent extends Object
{
    var $someVar = null;
    var $controller = true;

    function startup(&$controller)
    {
        // This method takes a reference to the controller which is loading it.
        // Perform controller initialization here.
    }

    function doFoo()
    {
        $this->someVar = 'foo';
    }
}

The startup() function is used by the Dispatcher during the CakePHP bootstrap process. Its a constructor-like function that allows a component access to its controller. If you do not want this function to be used or called, set the class variable $disableStartup to true.

Now, to use your component, you need to add the following code in your controller’s definition:

<?php
var $components = array('Foo');

Inside of that controller you could now use:

<?php
$this->Foo->doFoo();

A component gets access to the controller that loaded it through the startup() method shown above. This method is called immediately after Controller::beforeFilter(). This allows you to set component properties in the beforeFilter method, which the component can act on in it’s startup() method.

Because CakePHP loads models in a lazy fashion, it’s usually not a good idea to create model instances in components. If you need model data in a component, it’s best to pass that data in through one of the component’s methods:

<?php

class UsersController extends AppController
{
    var $uses = array('Apple');
    var $components = array('Foo');

    function index()
    {
        $data = $this->Foo->doFoo($this->Apple->findAll());
    }
}

You can also use other components inside your component. You simply have to declare in your component which components you want to use. In the example below it is the session component:

<?php
var $components = array('Session');

Making your components public

If you think your component can be helpful to others, add it to the Bakery. A component that becomes increasingly useful for the community may some day be included in the core distribution.

Also check the snippet archive for user committed components.