SQLAlchemy：如何创建 1:n 关系？ [复制]

Question

我即将使用 SQLAlchey 创建某种 1:n-realtionship。

我给你带来了两张照片，你可以看看这是怎么回事。首先，您将看到 EER 模型的图片。在这个 EER 模型中，我在 person 表和 family 表之间创建了 1:n 的关系。任何人都存储在 person 表中。我们都知道，人们可以彼此建立关系（母亲、父亲、女儿、儿子、堂兄、堂兄、侄子等）。为此，我设置了 family 表。

为了始终起到示范作用，我在表格中填满了虚构数据。查看家庭表，我们在第一列中看到中心人物，即 Hans Schmidt（ID 为 1）。在 Family 表中，以下人员通过外键保存：Kurt Schmidt（儿子）、Gerda Schmidt（妻子）、Gisela Schmidt（Hans 的母亲）和 Julia Schmidt（女儿）。我想指出汉斯·施密特的关系。

在我的源代码中，我已经将这个 ORM 模型映射如下：

class FAMILY(Base):

    __tablename__ = "family"

    id = Column(Integer, primary_key=True, unique=True, autoincrement=True)
    status = Column(String(255), nullable=False)

    person_id = Column(Integer, ForeignKey('person.id'))
    person = relationship("PERSON", backref='family', lazy='dynamic')

    family_person_id = Column(Integer, ForeignKey('person.id'))
    family_person = relationship("PERSON", backref='family', lazy='dynamic')


class PERSON(Base):

    __tablename__ = "person"

    id = Column(Integer, primary_key=True, unique=True, autoincrement=True)
    nickname = Column(String(255))
    alias_name  = Column(String (255))
    name_normally_used = Column(String(50), nullable=False)
    first_middle_name = Column(String(255))
    last_name = Column(String(100))

创建模型时，SQLAlchemy 不会导致任何问题（回显是真的，所以我可以跟踪它没有问题。）。但是，当我启动用户界面时，SQLAlchemy 会引发异常，您可以在其中管理人员的数据。

Traceback (most recent call last):
File "D:\Dan\Python\Xarphus\xarphus\subclass_master_data_load_data_item.py", line 140, in populate_item
self.populate_item_signal.emit(next(self._element))
File "D:\Dan\Python\Xarphus\xarphus\core\manage_data_manipulation_master_data.py", line 205, in select_all
for record in dict_store_session_query[category]():
File "D:\Dan\Python\Xarphus\xarphus\core\manage_data_manipulation_master_data.py", line 191, in <lambda>
'person_gender': lambda: self._session.query(PERSON_GENDER),
File "C:\Python27\lib\site-packages\sqlalchemy\orm\session.py", line 1362, in query
return self._query_cls(entities, self, **kwargs)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line 139, in __init__
self._set_entities(entities)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line 150, in _set_entities
self._set_entity_selectables(self._entities)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line 180, in _set_entity_selectables
ent.setup_entity(*d[entity])
File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line 3585, in setup_entity
self._with_polymorphic = ext_info.with_polymorphic_mappers
File "C:\Python27\lib\site-packages\sqlalchemy\util\langhelpers.py", line 764, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1948, in _with_polymorphic_mappers
configure_mappers()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 2869, in configure_mappers
raise e
InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers. Triggering mapper: 'Mapper|FAMILY|family'. Original exception was: Could not determine join condition between parent/child tables on relationship FAMILY.person - there are multiple foreign key paths linking the tables. Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference to the parent table.

Traceback (most recent call last):
File "D:\Dan\Python\Xarphus\xarphus\subclass_master_data_load_data_item.py", line 140, in populate_item
self.populate_item_signal.emit(next(self._element))
File "D:\Dan\Python\Xarphus\xarphus\core\manage_data_manipulation_master_data.py", line 205, in select_all
for record in dict_store_session_query[category]():
File "D:\Dan\Python\Xarphus\xarphus\core\manage_data_manipulation_master_data.py", line 194, in <lambda>
'person_title': lambda: self._session.query(PERSON_TITLE),
File "C:\Python27\lib\site-packages\sqlalchemy\orm\session.py", line 1362, in query
return self._query_cls(entities, self, **kwargs)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line 139, in __init__
self._set_entities(entities)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line 150, in _set_entities
self._set_entity_selectables(self._entities)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line 180, in _set_entity_selectables
ent.setup_entity(*d[entity])
File "C:\Python27\lib\site-packages\sqlalchemy\orm\query.py", line 3585, in setup_entity
self._with_polymorphic = ext_info.with_polymorphic_mappers
File "C:\Python27\lib\site-packages\sqlalchemy\util\langhelpers.py", line 764, in __get__
obj.__dict__[self.__name__] = result = self.fget(obj)
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1948, in _with_polymorphic_mappers
configure_mappers()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 2872, in configure_mappers
mapper._post_configure_properties()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\mapper.py", line 1765, in _post_configure_properties
prop.init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\interfaces.py", line 184, in init
self.do_init()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1654, in do_init
self._setup_join_conditions()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1729, in _setup_join_conditions
can_be_synced_fn=self._columns_are_mapped
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 1987, in __init__
self._determine_joins()
File "C:\Python27\lib\site-packages\sqlalchemy\orm\relationships.py", line 2114, in _determine_joins
% self.prop)
AmbiguousForeignKeysError: Could not determine join condition between parent/child tables on relationship FAMILY.person - there are multiple foreign key paths linking the tables. Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference to the parent table.

我们会在那里。 SQLALchey 显然对来自同一个表的两个外键有问题？给你的问题：如何建模才能最好地展示人与人之间的相互关系？因为经过我的推理，我至少需要 person 表中的两个外键，才能建立人员之间的关系。

Answer 1

您对映射器类FAMILY 的定义存在两个主要问题。

(1) 您已经两次将PERSON 引用为外键，因此您必须明确告诉SQLAlchemy 如何加入PERSON，请为每个关系设置foreign_keys 参数。

(2) 您使用了与backref 相同的值。 backref (FAMILY) 的值将成为 PERSON 类的属性名称。查看您的FAMILY，有两个属性分别名为person 和family_person，那么PERSON 类应该有两个不同的属性。

另外，在您的代码中，FAMILY 和 PERSON 之间的关系是多对一的，因此 dynamic 值对于参数 lazy 无效，您应该使用默认值。下面是示例代码：

class FAMILY(Base):

    __tablename__ = "family"

    id = Column(Integer, primary_key=True, unique=True, autoincrement=True)
    status = Column(String(255), nullable=False)

    person_id = Column(Integer, ForeignKey('person.id'))
    person = relationship("PERSON", backref='family_to',
                          foreign_keys=[person_id],
                          )

    family_person_id = Column(Integer, ForeignKey('person.id'))
    family_person = relationship("PERSON",
                                 foreign_keys=[family_person_id],
                                 backref='family_from')

这里有一些与您的问题相关的有用链接：Refer a table twice、Relationship configration

谢谢！