django查询以获取数据

我陷入了一个非常混乱的境地,我有一对多的关系,我想要查询数据,就像我想要所有父表数据,但只想从满足site_id=100条件的子表中获取数据一样。

class Policy(Base):
    """table containing details for Policies"""
    __tablename__ = "UmbrellaPolicy"
    id = Column(Integer, primary_key=True)
    policy_id = Column(Integer, nullable=False, index=True)
    user_defined_name = Column(String(255), nullable=True)

孩子就是这样

class Site(Base):
    __tablename__ = "Site"
    id = Column(Integer, primary_key=True)
    policy_id = Column(Integer, ForeignKey("Policy.id"))
    site_id = Column(String(32), nullable=False, index=True)
    policy = relationship("Policy", backref="sites")