code: func (mc MongoClient) getValueDescriptors(q bson.M) ([]models.ValueDescriptor, error) {
  	s := mc.getSessionCopy()
  	defer s.Close()
  
  	var v []models.ValueDescriptor
  	if err := s.DB(mc.database.Name).C(db.ValueDescriptorCollection).Find(q).All(&v); err != nil {
  		return []models.ValueDescriptor{}, errorMap(err)
  	}
  	return v, nil
  }
docs: // Get value descriptors based on the query