与 MySQL 一起使用的 SQLAlchemy 关系在与 Sql Server 一起使用时会生成错误

Question

我有一些使用 MySQL 的 SQLAlchemy ORM 代码，但是当我将底层数据库更改为 Sql Server 时，我收到消息 Module 'user_group' has no mapped classes registered under the name 'foreign_keys'

这是其中一个主要类的 ORM 定义：

class User(Base):
    __tablename__ = 'user'
    __table_args__ = (
        {'schema':'admn'}
    )

    user_id = Column(Integer, autoincrement=True, primary_key=True)
    user_name = Column(Unicode(255), unique=True, nullable=False)
    _password = Column('password', Unicode(80), nullable=True)
    authentication_backend = Column(Unicode(255), nullable=False, default='application_db')

    groups = relationship(
        "Group",
        secondary="user_group",
        back_populates="users",
        cascade="all", passive_deletes = True)

这是另一个主类的定义：

class Group(Base):
    __tablename__ = 'group'
    __table_args__ = (
        {'schema': 'admn'}
    )

    group_id = Column(Integer, autoincrement=True, primary_key=True)
    name = Column(Unicode(255), unique=True, nullable=False)
    description = Column(Unicode(255), unique=True, nullable=True)

    users = relationship(
        "User",
        secondary="user_group",
        back_populates="groups",
        cascade="all",
        passive_deletes=True) 

以及与它们相关的次要类：

class UserGroup(Base):
    __tablename__ = 'user_group'
    __table_args__ = (
        {'schema': 'admn'}
    )

    user_id = Column(Integer, ForeignKey('user.user_id', ondelete="cascade", onupdate="cascade"), primary_key = True)
    group_id = Column(Integer, ForeignKey('group.group_id', ondelete="cascade", onupdate="cascade"), primary_key = True)

知道为什么我在 SQL Server 中收到此错误消息而不是在 MySql 中吗？？

迈克尔

相关追溯：

    user = Session.query(User).filter(User.user_name==user_name).first()
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/scoping.py", line 153, in do
    return getattr(self.registry(), name)(*args, **kwargs)
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/session.py", line 1393, in query
    return self._query_cls(entities, self, **kwargs)
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/query.py", line 140, in __init__
    self._set_entities(entities)
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/query.py", line 151, in _set_entities
    self._set_entity_selectables(self._entities)
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/query.py", line 181, in _set_entity_selectables
    ent.setup_entity(*d[entity])
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/query.py", line 3619, in setup_entity
    self._with_polymorphic = ext_info.with_polymorphic_mappers
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/util/langhelpers.py", line 767, in __get__
    obj.__dict__[self.__name__] = result = self.fget(obj)
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/mapper.py", line 1994, in _with_polymorphic_mappers
    configure_mappers()
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/mapper.py", line 3013, in configure_mappers
    mapper._post_configure_properties()
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/mapper.py", line 1811, in _post_configure_properties
    prop.init()
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/interfaces.py", line 184, in init
    self.do_init()
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/relationships.py", line 1656, in do_init
    self._setup_join_conditions()
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/relationships.py", line 1731, in _setup_join_conditions
    can_be_synced_fn=self._columns_are_mapped
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/relationships.py", line 1998, in __init__
    self._determine_joins()
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/orm/relationships.py", line 2065, in _determine_joins
    consider_as_foreign_keys=consider_as_foreign_keys
  File "<string>", line 2, in join_condition
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/sql/selectable.py", line 964, in _join_condition
    a, a_subset, b, consider_as_foreign_keys)
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/sql/selectable.py", line 996, in _joincond_scan_left_right
    b.foreign_keys,
  File "/home/michaell/projects/ddp_ve/lib/python3.5/site-packages/sqlalchemy/ext/declarative/clsregistry.py", line 198, in __getattr__
    self.__parent.name, key))
AttributeError: Module 'user_group' has no mapped classes registered under the name 'foreign_keys'

Answer 1

除了将 SQL Server 架构名称作为表 args 的一部分提及之外，如下所示：

class UserGroup(Base):
    __tablename__ = 'user_group'
    __table_args__ = (
        {'schema': 'admn'}
)

架构名为“admn”。

您还必须在您命名表的 ORM 中的各种字符串中提及架构名称。到目前为止我发现了两个例子：

外键：

    user_id = Column(Integer, ForeignKey('admn.user.user_id', ondelete="cascade", onupdate="cascade"), primary_key = True)

在您提及表时的关系中，例如辅助表：

  users = relationship(
        "User",
        secondary="admn.user_group",
        back_populates="groups",
        cascade="all",
        passive_deletes=True) 

这是导致我的映射器错误的最后一个地方。 IE 在secondary=...中提到架构名称后，映射器错误就消失了。