models.py

## Models.py
class Message (MarkDeleted):
    uuid    = db.StringProperty (required=True)
    owner   = db.ReferenceProperty (Actor, collection_name="message_owner", required=True)
    target  = db.ReferenceProperty (Actor, collection_name="message_target", required=True)

    entry  = db.ReferenceProperty (Entry, required=True)
    reply  = db.SelfReferenceProperty ()

    label  = db.StringProperty (choices=MESSAGE_LABEL, required=True)

    readed  = db.BooleanProperty (default=False) # Message lu/non lu                                                                                                                                   
    trashed = db.BooleanProperty (default=False) # Message Supprimer dans la poubelle ou non                                                                                                           

    key_template = "%(label)s/%(owner)s/%(uuid)s"

## Index.yaml
- kind: Message
  properties:
  - name: deleted
  - name: label
  - name: readed
  - name: target
  - name: trashed
  - name: created

## Query, Why i need a composite index?
query = Message.all ()
query.filter (label =', 'receive')
query.filter ('deleted =', None)
query.filter ('trashed =', False)
query.filter ('target =', actor)
query.filter ('readed =', False)
print query.count ()