code: async def create_app_collections(db):
      ''' load all models in app and create collections in db with specified indices'''
      futures = []
      for model_class in MongoCollectionMixin.__subclasses__():
          if model_class._meta.concrete is True:
              futures.append(create_collection(db, model_class))
  
      await asyncio.gather(*futuresync def create_app_collections(db):
      ''' load all models in app and create collections in db with specified indices'''
      futures = []
      for model_class in MongoCollectionMixin.__subclasses__():
          if model_class._meta.concrete is True:
              futures.append(create_collection(db, model_class))
  
      await asyncio.gather(*futures)
docs: load all models in app and create collections in db with specified indices