public function configure()
 {
     unset($this['student_school_year_list']);
     sfContext::getInstance()->getConfiguration()->loadHelpers(array('Asset', 'Tag', 'Url'));
     //widgets
     $this->widgetSchema['year'] = new sfWidgetFormInput(array());
     $date = SchoolYearPeer::suggestYear();
     $this->widgetSchema['year']->setDefault($date);
     //validators
     $this->validatorSchema['year'] = new sfValidatorInteger(array('max' => 9999, 'min' => 1900));
     $this->validatorSchema['year']->addMessage('max', '"%value%" debe ser menor a %max%.');
     $this->validatorSchema['year']->addMessage('min', '"%value%" debe ser mayor a  %min%.');
     $this->validatorSchema['year']->addMessage('invalid', 'Debe ingresar un número.');
     $this->validatorSchema->setPostValidator(new sfValidatorPropelUnique(array('model' => 'SchoolYear', 'column' => 'year'), array('invalid' => 'El año lectivo ya existe en el sistema.')));
 }