Defining global conditions in Model

Question

Is it possible to define global conditions for Model ?

I have 2 Models: User and Student. In database both of them are using table users but each student has set parent_id to its owner (which is set in the same table) while each user has parent_id set to Null.

When I use for example

$this->find('all'); 

in Student Model I want to force Cake to return only those records from database table users where parent_id != Null .

So the question is - can I define somehow global conditions in the Model? Something like that:

public $conditions = array('Student.parent_id !=' => Null);

Answer 1

Use beforeFind

You can use before find to modify all queries issued for a model:

function beforeFind(array $queryData) {
    $queryData['conditions'][]['NOT'][$this->alias . '.parent_id'] = null;
    return $queryData;
}

Be careful using this technique to not overwrite existing conditions (note the extra []) otherwise a query for "not parent_id 2" becomes "not parent_id null".