如何约束SQLAlchemy关系的“多”方面的对象数量？

Question

给出一个类似于SQLAlchemy文档（http://docs.sqlalchemy.org/en/rel_1_0/orm/tutorial.html#building-a-relationship）中的关系模式：

from sqlalchemy import *
from sqlalchemy.orm import relationship


class User(Base):
    __tablename__ = 'user'
    id = Column(Integer, primary_key=True)


class Address(Base):
    __tablename__ = 'address'
    id = Column(Integer, primary_key=True)
    email_address = Column(String)
    user_id = Column(Integer, ForeignKey('user.id'))

    user = relationship('User', backref='addresses')

有没有办法限制User个实例必须至少有一个Address？

换句话说，这应该失败：

user = User()
session.add(user)
session.commit()

......虽然这应该成功：

user = User()
address1 = Address(email_address='example1@example.com')
address2 = Address(email_address='example2@example.com')
user.addresses = [address1, address2]
session.add(user)
session.commit()