class User(db.Model):  # Todo create a user model, that works with your login page
    username = db.UserProperty()
    password = db.StringProperty()

class BlogPost(ndb.Model):
    title = ndb.StringProperty()
    content = ndb.TextProperty()
    timestamp = ndb.DateTimeProperty(auto_add_now=True)

# Then you can specify a parent in the constructor (where user is a User entity)
blog_post = BlogPost(parent=user)
blog_post.title = 'Post title'
blog_post.content = 'Post content'
blog_post.put()