Cloud NDB: transactionally put() multiple entities

Question

There are situations where we must save two or more datastore entities at once (either both entities are saved or neither is saved). For my example, I want to create a UserProfile entity when a User entity is created.

from entities import User, UserProfile

def create_user_and_profile():
    # First, create the User entity
    user = User(email=email, password=password_hash)
    user.put()

    # Then, create a UserProfile entity
    # that takes a user.key as parent
    user_profile = UserProfile(parent=user.key)
    user_profile.put()

The function above is not atomic. It is possible that only one or neither of the entities are saved successfully.

How can I make this atomic?

Answer 1

there's transactional decorator in ndb you can use. If any of the records would fail to be saved, none of them will:

from google.cloud import ndb


@ndb.transactional()
def create_user_and_profile():
    # First, create the User entity
    user = User(email=email, password=password_hash)
    user.put()

    # Then, create a UserProfile entity
    # that takes a user.key as parent
    user_profile = UserProfile(parent=user.key)
    user_profile.put()

with ndb_client.context(): # ndb client instance
    create_user_and_profile()