SQLAlchemy：如何创建1：n关系？

Question

我即将使用SQLAlchey创建一个特定的1：n-realtionship。

我为你带了两张照片，所以你可以看到这是什么。首先，您将看到EER模型的图片。在此EER模型中，我在 person 表和 family 表之间创建了1：n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......）。出于这个原因，我已经设置了 family 表。

为了让整个时间充当示范，我用虚拟数据填充了表格。看一下家庭表，我们在第一栏中看到，这是中心人物，即Hans Schmidt（ID为1）。在家庭表中，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Hans Schmidt的关系。

在我的源代码中，我已按如下方式映射此ORM模型：

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不会引起任何问题（echo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会抛出异常，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显然有来自同一个表的两个外键的问题？问题：如何最好地进行建模以显示人与人之间的相互关系？因为在我推理之后，我需要人员表中至少有两个外键，以便在人员之间建立关系。

Answer 1

您对mapper类FAMILY的定义存在两个主要问题。

（1）您已将PERSON作为外键引用两次，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FAMILY，有两个名为person和family_person的属性，那么PERSON类应该有两个不同的属性。

此外，在您的代码中，FAMILY和PERSON之间的关系很多，因此dynamic值对参数lazy无效，您应该使用默认值。以下是示例代码：

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')

以下是与您的问题相关的一些有用链接：Refer a table twice，Relationship configration

谢谢！