How to specify the class for Doctrine ODM Collection mapping types

I have a document with a field marked for persistence as a Collection

 use Doctrine\ODM\MongoDB\Mapping\Annotations as ODM;  

/** @ODM\Document */
class Item
{
    /**
    * @ODM\Collection
    */
    protected $things;

}

By default, when Doctrine maps the values from Mongo it will set $things to be an instance of Doctrine\Common\Collections\ArrayCollection.

This violates my domain model however as my domain objects expect the $things property to be an instance of my own collection class ThingsCollection. This class does various validations on the list of things.

How can I tell Doctrine to use my ThingsCollection class instead? I imagine I will have to make the ThingsCollection class implement the Doctrine\Common\Collections\Collection interface but that is not a problem if I can just figure out how to tell Doctrine about the mapping in the first place.

Solution

The answer is that it is not possible.

Furthermore, despite the documentation being confusing and saying otherwise, for a general Collection property mapping as above (not a reference) an ArrayCollection is not returned. A basic php array is given.

So, it appears in this situation, you are forced to work with arrays, at least currently.