Insert data with Zend_Form and Zend_Db_Table many-to-many

// [ Database ]

// Manager.php

class Application_Model_DbTable_Manager extends Zend_Db_Table_Abstract {

    protected $_name = 'managers';

    protected $_dependentTables = array('Application_Model_DbTable_ManagerProject');

    public function findManager($role) {
        $select = $this->select();
        $select->where('role = ?', $role);
        return $this->fetchAll($select);
    }
}


// Project.php

class Application_Model_DbTable_Project extends Zend_Db_Table_Abstract {

    protected $_name = 'projects';

    protected $_dependentTables = array('Application_Model_DbTable_ManagerProject');

}




// ManagerProject.php

class Application_Model_DbTable_ManagerProject extends Zend_Db_Table_Abstract {

    protected $_name = 'managers_projects';

    protected $_referenceMap = array(
        array(
            'columns' => array('id_managers_managers'),
            'refTableClass' => 'Application_Model_DbTable_Manager',
            'refColumns' => array('id_manager')
        ),
        array(
            'columns' => array('id_projects_projects'),
            'refTableClass' => 'Application_Model_DbTable_Project',
            'refColumns' => array('id_project')
        )
    );

}





//[ Form ]

//Project.php

class Application_Form_Project extends Zend_Form {


    public function init() {

        $idProject = Zend_Form_Element_Hidden('id_project');

        $nameProject = Zend_Form_Element_Text('name_project');

        $managers = Zend_Form_Element_MultipleSelect('id_manager');

        $table = new Application_Model_DbTable_Manager();

            foreach($table->findManager('manager') as $object) {
                    $managers->addMultiOption($object->id_manager, $object->name);
            }

        $submit = new Zend_Form_Element_Submit('submit');

        $this->addElements(array($idProject, $nameProject, $managers, $submit));

    }

}


// [ Controller ]

//ProjectController.php

class ProjectController extends Zend_Controller_Action {


    public function addAction()
    {
        $form = new Application_Form_Project();
        $this->view->form = $form;

        if($this->getRequest()->isPost()) {
            if($form->isValid($this->getRequest()->getPost())) {

                $databaseProject = new Application_Model_DbTable_Project();


        /**
        * How do I include in table many-to-many?
        *
        *
        *
        */



            }
        }

        $this->view->form = $form;
    }

}