doctrine ODM / Mongo DB and Object References

Question

for the life of me, I can not find the answer to this problem. So, I'll ask here.

Let's say I have 3 document types in my mongo.

// provider
{
   $id: ObjectId('xxx'),
   "name": "some name",
}

// category
{
   $id: ObjectId('yyy'),
   "name": "some category"
}

// item
{
  $id: ObjectId('zzz'),
  "name": "some item",
  "references": { 
     "provider": {
        $ref: "provider",
        $id: ObjectId('xxx')
     },
     "category": [
         {
             $ref: "category",
             $id: ObjectId('yyy')
         }
         // etc etc, more referenced categories
     ]
  }
}

Now, how would I annotate my Doctrine entity so I can read out and simply query the referenced objects. For clarity I really would like to keep all the external references within the "references" block.

Any help would be greatly appreciated.

Marc