Remove null values coming from empty collection form item

Question

I'm trying to implement a ManyToMany relation in a form between 2 entities (say, Product and Category to make simpe) and use the method described in the docs with prototype and javascript (http://symfony.com/doc/current/cookbook/form/form_collections.html).

Here is the line from ProductType that create the category collection :

$builder->add('categories', 'collection', array(
                   'type' => 'entity',
                   'options' => array(
                        'class' => 'AppBundle:Category',
                        'property'=>'name',
                        'empty_value' => 'Select a category',
                        'required' => false),
                   'allow_add' => true,
                   'allow_delete' => true,
              ));

When I had a new item, a new select appear set to the empty value 'Select a category'. The problem is that if I don't change the empty value, it is sent to the server and after a $form->bind() my Product object get some null values in the $category ArrayCollection.

I first though to test the value in the setter in Product entity, and add 'by_reference'=>false in the ProductType, but in this case I get an exception stating that null is not an instance of Category.

How can I make sure the empty values are ignored ?

Answer 1

Citing the documentation on 'delete_empty':

If you want to explicitly remove entirely empty collection entries from your form you have to set this option to true

$builder->add('categories', 'collection', array(
               'type' => 'entity',
               'options' => array(
                    'class' => 'AppBundle:Category',
                    'property'=>'name',
                    'empty_value' => 'Select a category'),
               'allow_add' => true,
               'allow_delete' => true,
               'delete_empty' => true
          ));

Since you use embedded forms, you could run in some issues such as Warning: spl_object_hash() expects parameter 1 to be object, null given when passing empty collections.

Removing required=>false as explained on this answer did not work for me.

A similar issue is referenced here on github and resolved by the PR 9773