Cakephp - $this->displayField not seting

I am having an issue with cakephp 1.2.5 where i am setting $displayField in my model but when i call $this->displayField from within "/app/app_model.php" it is returning id.

My Model is

class Trainer extends AppModel {
    var $name = 'Trainer';
    var $displayField = 'name';

An example of my app_model would be

class AppModel extends Model {
    function beforeSave() {
        print $this->displayField;
        return true;