Mongo_Model::init PHP Method

    public function init()
    {
        parent::init();
        $this->setSource('Mongo');
        $this->addField('_id')->system(true);
    }

 function init()
 {
     parent::init();
     $this->addField('name');
     $this->addField('sex')->enum(array('M', 'F'))->defaultValue('M');
 }