RedBull RIS - populate example

class BaseModel(ndb.Model):
  @classmethod
  def populate(cls, key):
    self = key.get()
    sources = getattr(self.__class__, 'sources', False)
    source_data = {}
    if not sources:
      return False
    for source_name in sorted(sources.keys(), key=lambda k: 0 if k == 'gplus' else 9):
      source_id_property = 'source_id_' + source_name
      entity_source_id = getattr(self, source_id_property, False)
      if not entity_source_id:
        continue
      try:
        data = source.load(self.__class__.__name__, entity_source_id, self)
        source_data[source_name] = data
      except:
        logging.warn('Error loading source')
        setattr(self, 'source_failed_' + source_name, True)

    self.update_data(source_data)
    return self

  def put(self, *args, **kwargs):
    # execute all the logic needed to populate the model, then:
    if do_populate:
      deferred.defer(self.__class__.populate, self.key, _queue='populate-entity')
    if self.__class__.__name__ != 'Connection':
      deferred.defer(Connection.update_connections, self.key)


  class Artist(BaseModel):
  """an artist"""
  sources = {
    'gplus': {
      'properties': {
        'content': ['/aboutMe'],
        'blob_key_image': ['/image/url', '/cover/coverPhoto/url'],
        'website': ['/url', '/urls/value'],
        'source_id_gplus': ['/id'],
        'source_rating_gplus': ['/circledByCount'],
      },
    },
    'freebase': {
      'properties': {
        'content': ['/common/topic/description', '/common/topic/article'],
        'address': ['/people/person/place_of_birth'],
      },
    },
    'discogs': {
      'properties': {
        'content': ['/profile'],
        'website': ['/urls'],
        'blob_key_image': ['/images'],
        'aliases': ['/aliases'],
        'source_id_discogs': ['/id'],
      },
    },
    'soundcloud': {
      'properties': {
        'source_rating_soundcloud': ['/followers_count'],
      },
    },
    'lastfm': {
      'properties': {
        'content': ['/bio/content'],
        'website': ['/url', '/website'],
        'blob_key_image': ['/image[size=extralarge]/#text'],
        'active_from': ['/bio/yearformed'],
        'source_id_lastfm': ['/mbid'],
        'source_rating_lastfm': ['/stats/listeners'],
      },
    },
  }

  name = ndb.StringProperty()
  content = ContentProperty(ndb.TextProperty)
  address = ContentProperty(ndb.TextProperty)
  blob_key_image = ContentProperty(ndb.BlobKeyProperty)
  active_from = ContentProperty(ndb.DateProperty)
  website = ContentProperty(ndb.StringProperty, repeated=True)
  aliases = ContentProperty(ndb.StringProperty, repeated=True)