generated.sql

CREATE TABLE user_accounts (
  id VARCHAR(25) NOT NULL, 
  -- ... snip
	PRIMARY KEY (id), 
)

CREATE TABLE user_blogsettings (
  id INTEGER NOT NULL AUTO_INCREMENT, 
	user_id VARCHAR(128), 
  -- ... snip 
	PRIMARY KEY (id), 
	FOREIGN KEY(user_id) REFERENCES user_accounts (id) ON DELETE CASCADE
)

models.py

class User(ModelBase, AuthUser):
    """
    Implementation of User for persistence in Google's App Engine datastore.
    """
    __tablename__ = 'user_accounts'
    __public__ = ['uid', 'name', 'email', 'irc', 'phone', 'tz']

    id = sa.Column(sa.String(25), primary_key=True)

    # ... snip

    blog = relationship('models.UserBlogSettings', uselist=False,
        backref='user', cascade="all, delete-orphan",
        passive_deletes=True)
  
  
  class UserBlogSettings(ModelBase):
    __tablename__ = 'user_blogsettings'

    id = sa.Column(sa.Integer, primary_key=True)
    user_id = sa.Column(sa.String(128),
        sa.ForeignKey('user_accounts.id', ondelete='CASCADE'))