Symfony2中MongoDB的日期下拉？

I am trying to list specific dates from MongoDB database, from a custom query, in a select (dropdown) field using Symfony 2, using entity (document) form type.

I am trying the following:

$defaultData = array();
    $form = $this->createFormBuilder($defaultData)
                ->add('date', 'document', array(
                    'class' => 'MyBundle:Items',
                    'property' => 'date',
                    'query_builder' => function(DocumentRepository $dr) {
                        return $dr->createQueryBuilder('Items')
                            ->field('user')->references($this->getUser());
                    },
                ))
                ->add('Search', 'submit')
                ->getForm();

This returns error "Object of class DateTime could not be converted to string" in twig template.

Is there a way to format DateTime to string in form output, or is there a way to achieve this with a date field? Any help and an example is highly appreciated. Thank you.

You should just add a method that returns date formatted as you wish:

class Items 
{
     private $date;
     //....
     public function getDate()
     {
          return $this->date;
     }
     //....
     public function getDateString()
     {
          return $this->date->format('d-m-Y');
     }
     //....

And the just use that method as property in your form field:

->add('date', 'document', array(
      'class' => 'MyBundle:Items',
      'property' => 'date_string',