code: func (mc MongoClient) DBRefToReading(dbRef mgo.DBRef) (a models.Reading, err error) {
  	if err = mc.database.C(db.ReadingsCollection).Find(bson.M{"_id": dbRef.Id}).One(&a); err != nil {
  		return models.Reading{}, errorMap(err)
  	}
  	return
  }
docs: // ************************ READINGS ************************************8