I had this idea a while ago, and actually implemented it into a Cake project, but it was a bit hacky and required hacking the core. So I didn't like it. But today, I had a need for this same functionality, so I had a little think about how I could implement it without hacking the core, and thus was born the Callbacks plugin for CakePHP.

If any of you have ever used Ruby on Rails, you should be familiar with its callback system. Well, it was this system that I needed.  I just started fleshing out a new Cake app, and needed to run a beforeFilter callback on a couple of specific controller actions. Of course, I could do this:

class MyController extends AppController {
    function beforeFilter() {
        if ($this->params['action'] == 'index' || $this->params['action'] == 'view') {
            # do something here that only the 'index' and 'view' actions need
        }
    }
}

But that's just not very elegant, and will get pretty messy the more you do it. So I came up with the Callback plugin, which is basically a simple component that provides some sweetly fine grained control over your callbacks. So now I can do this instead:

  class MyController extends AppController {
      var $beforeFilter = array('myCallback');

      function _myCallback() {
          # do something here
      }
  }

and I can even call several callbacks, each with their own methods:

  class MyController extends AppController {
      var $beforeFilter = array('myCallback', 'anotherCallback', 'andAnotherOne');

      function _myCallback() {
          # do something here
      }

      function _anotherCallback() {
          # do something here
      }

      function _andAnotherOne() {
          # do something here
      }

Now the above is lovely and all, but it doesn't really provide any extra functionality above what Cake already provides. So far, my code just looks cleaner. What I really want to do is only run the anotherCallback when calling the index action. So I change the $beforeFilter param:

  class MyController extends AppController {
      var $beforeFilter = array(
          'myCallback',
          'anotherCallback' => array(
              'only' => 'index'
          )
          'andAnotherOne'
      );

Much better! I can also specify to run a callback on all actions, except the 'delete' action:

  class MyController extends AppController {
      var $beforeFilter = array(
          'anotherCallback' => array(
              'except' => 'delete'
          )
      );

Even better! But still I wanted more!

I wanted to be able to add even more control, and only run a callback if a certain condition is/not met:

  class MyController extends AppController {
      var $beforeFilter = array(
          'anotherCallback' => array(
              'if' => 'ifTrue'
          )
      );

      function _ifTrue() {
          # do something here and return true for the callback to run
          return true;
      }

So the anotherCallback callback will now only run if the _ifTrue method returns true. Lovely!

Right now it supports the three main controller callbacks: beforeFilter, beforeRender and afterFilter. The plan is to provide the same functionality to Models.

You can checkout the code from Codaset repo at http://codaset.com/joelmoss/cakephp-callbacks. Feel free to fork away!