Use a custom ID type in mongodb usyng python -

I am using a memodab as a storage backend for some of my information in a Django 1.5 app.

Each document stored in the Mongodb archive has a _id field that is a decrypt made of several strings. Now when I try to recover this information, I map the document in a model class using the Mongoengine: ago>

I can see: < TypeError

  type 
  document = MyClass.objects print document   
 The error / view name / id should be an example (str, unicode, object), no & lt; Type 'dict' & gt;   
 The worse is that when I use to save the writings  
  obj = MyClass ({"tag": "sometag"}) Obj.save ()   
 I get the same error, but  _id = {"tag": "sometag"}  was created in the DB archive. > 
 What could be any thoughts? It may be that this is the case.  
 Note: I tried to use Embedded Documentfield but the results are the same (error takes the name of my embedded class instead of 'encrypted')   
 
 
 I found:  
 I was missing the  primary_key  argument if I Change it to model:  
  Class MyClass (document): id = DictField (primary_key = true)   
 It starts working on both operations , Read Write more.  
 Here is the official doctor: