多对多关联表上的 SQLAlchemy 关系

Question

我正在尝试建立与另一个多对多关系的关系，代码如下所示：

from sqlalchemy import Column, Integer, ForeignKey, Table, ForeignKeyConstraint, create_engine
from sqlalchemy.orm import relationship, backref, scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

supervision_association_table = Table('supervision', Base.metadata,
    Column('supervisor_id', Integer, ForeignKey('supervisor.id'), primary_key=True),
    Column('client_id', Integer, ForeignKey('client.id'), primary_key=True)
)

class User(Base):
    __tablename__ = 'user'

    id = Column(Integer, primary_key=True)

class Supervisor(User):
    __tablename__ = 'supervisor'
    __mapper_args__ = {'polymorphic_identity': 'supervisor'}

    id = Column(Integer, ForeignKey('user.id'), primary_key = True)

    schedules = relationship("Schedule", backref='supervisor')

class Client(User):
    __tablename__ = 'client'
    __mapper_args__ = {'polymorphic_identity': 'client'}

    id = Column(Integer, ForeignKey('user.id'), primary_key = True)

    supervisor = relationship("Supervisor", secondary=supervision_association_table,
                                backref='clients')
    schedules = relationship("Schedule", backref="client")

class Schedule(Base):
    __tablename__ = 'schedule'
    __table_args__ = (
        ForeignKeyConstraint(['client_id', 'supervisor_id'], ['supervision.client_id', 'supervision.supervisor_id']),
    )

    id = Column(Integer, primary_key=True)
    client_id = Column(Integer, nullable=False)
    supervisor_id = Column(Integer, nullable=False)

engine = create_engine('sqlite:///temp.db')
db_session = scoped_session(sessionmaker(bind=engine))
Base.metadata.create_all(bind=engine)

我想做的是将计划与特定的客户主管关系相关联，尽管我还没有找到如何做它。通过查看 SQLAlchemy 文档，我发现了一些提示，导致 Schedule-Table 上出现了foreignkeyconstraint。

我如何指定关系才能使该关联发挥作用？

Answer 1

您需要映射 supervision_association_table 以便您可以创建与它的关系。

我可能在这里掩盖了一些东西，但看起来既然你在这里有多对多，你真的不能有 Client.schedules - 如果我说 Client.schedules.append( some_schedule)，它指向“supervision”中的哪一行？

下面的示例为那些加入每个 SupervisorAssociation 的 Schedule 集合的访问器提供了一个只读“rollup”访问器。 association_proxy 扩展用于在方便时隐藏 SupervisionAssociation 对象的详细信息。

from sqlalchemy import Column, Integer, ForeignKey, Table, ForeignKeyConstraint, create_engine
from sqlalchemy.orm import relationship, backref, scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.associationproxy import association_proxy
from itertools import chain

Base = declarative_base()

class SupervisionAssociation(Base):
    __tablename__ = 'supervision'

    supervisor_id = Column(Integer, ForeignKey('supervisor.id'), primary_key=True)
    client_id = Column(Integer, ForeignKey('client.id'), primary_key=True)

    supervisor = relationship("Supervisor", backref="client_associations")
    client = relationship("Client", backref="supervisor_associations")
    schedules = relationship("Schedule")

class User(Base):
    __tablename__ = 'user'

    id = Column(Integer, primary_key=True)

class Supervisor(User):
    __tablename__ = 'supervisor'
    __mapper_args__ = {'polymorphic_identity': 'supervisor'}

    id = Column(Integer, ForeignKey('user.id'), primary_key = True)

    clients = association_proxy("client_associations", "client", 
                        creator=lambda c: SupervisionAssociation(client=c))

    @property
    def schedules(self):
        return list(chain(*[c.schedules for c in self.client_associations]))

class Client(User):
    __tablename__ = 'client'
    __mapper_args__ = {'polymorphic_identity': 'client'}

    id = Column(Integer, ForeignKey('user.id'), primary_key = True)

    supervisors = association_proxy("supervisor_associations", "supervisor", 
                        creator=lambda s: SupervisionAssociation(supervisor=s))
    @property
    def schedules(self):
        return list(chain(*[s.schedules for s in self.supervisor_associations]))

class Schedule(Base):
    __tablename__ = 'schedule'
    __table_args__ = (
        ForeignKeyConstraint(['client_id', 'supervisor_id'], 
        ['supervision.client_id', 'supervision.supervisor_id']),
    )

    id = Column(Integer, primary_key=True)
    client_id = Column(Integer, nullable=False)
    supervisor_id = Column(Integer, nullable=False)
    client = association_proxy("supervisor_association", "client")

engine = create_engine('sqlite:///temp.db', echo=True)
db_session = scoped_session(sessionmaker(bind=engine))
Base.metadata.create_all(bind=engine)

c1, c2 = Client(), Client()
sp1, sp2 = Supervisor(), Supervisor()
sch1, sch2, sch3 = Schedule(), Schedule(), Schedule()

sp1.clients = [c1]
c2.supervisors = [sp2]
c2.supervisor_associations[0].schedules = [sch1, sch2]
c1.supervisor_associations[0].schedules = [sch3]

db_session.add_all([c1, c2, sp1, sp2, ])
db_session.commit()


print c1.schedules
print sp2.schedules