sqlalchemy嵌套对象关系急切加载

Question

如何从C加载所有相关类C.B.A

1）一个典型的查询（使用两个连接） VS 2）急切加载

class A(Base):
    __tablename__ = 'a'



class B(Base):
    __tablename__ = 'b'
    id = Column(Integer, primary_key=True)
    a_id = Column(Integer, ForeignKey('a.id'))

    a = relationship(A)


class C(Base):
    __tablename__ = 'c'
    id = Column(Integer, primary_key=True)
    b_id = Column(Integer, ForeignKey('b.id'))

    b = relationship(B)