Create a file named app_model.php and place it in your app/ folder, with the following contents. If you already have one, make sure that either you add the actsAs property shown as follows, or that your actsAs property includes Containable.

<?php
class AppModel extends Model {
public $actsAs = array('Containable');
}
?>

The Containable behavior is nothing more and nothing less than a wrapper around the bindModel() and unbindModel() methods, defined in the CakePHP's Model class. It is there to help us deal with the management of associations without having to go through a lengthy process of redefining all the associations when calling one of these methods, thus making our code much more readable and maintainable.

This is a very important point, because a common mistake CakePHP users make is to think that Containable is involved in the query-making process, that is, during the stage where CakePHP creates actual SQL queries to fetch data.

Containable saves us some unneeded queries, and optimizes the information that is fetched for each related model, but it will not serve as a way to change how queries are built in CakePHP.