我与sqlalchemy建立了多对多的关系,如下所示:
subject_books = Table('subject_books', Base.metadata,
Column('subject_id', Integer, ForeignKey('subjects.id')),
Column('book_id', Integer, ForeignKey('books.id')),
Column('group', Integer)
)
class Subject(Base):
__tablename__ = 'subjects'
id = Column(Integer, primary_key=True)
value = Column(Unicode(255), unique=True)
class Book(Base):
__tablename__ = 'books'
id = Column(Integer, primary_key=True)
title = Column(Unicode(255))
isbn = Column(Unicode(24))
subjects = relationship('Subject', secondary=subject_books, collection_class=attribute_mapped_collection('group'), backref='books')
之后,我创建了如下测试:
book = Book(title='first book',isbn='test')
book.subjects[0] = Subject(value='first subject')
book.subjects[1] = Subject(value='second subject')
session.add(book)
transaction.commit()
而且效果很好。但我真正想要的是存储多个具有相同组值的受试者,所以我尝试了以下测试:
book = Book(title='first book',isbn='test')
book.subjects[0] = [Subject(value='first subject'),Subject(value='second subject')]
book.subjects[1] = [Subject(value='third subject'),Subject(value='forth subject')]
session.add(book)
transaction.commit()
但它不起作用。
这可以用sqlalchemy完成吗?
提前谢谢
最佳答案
拉济
我认为你在建立错误的关系。
你的关系一定是
预订M2M主题
主题M2M组
因此,您必须为group再创建一个模型,该模型必须在Subject中指定为m2m
你的模特会喜欢的。
subject_books = Table('subject_books', Base.metadata,
Column('subject_id', Integer, ForeignKey('subjects.id')),
Column('book_id', Integer, ForeignKey('books.id')),
)
subject_group = Table('subject_groups', Base.metadata,
Column('group_id', Integer, ForeignKey('groups.id')),
Column('subject_id', Integer, ForeignKey('subjects.id')),
)
class Subject(Base):
__tablename__ = 'subjects'
id = Column(Integer, primary_key=True)
value = Column(Unicode(255), unique=True)
groups = relationship('Groups', secondary=subject_groups, backref='subjects')
class Groups(Base):
__tablename__ = 'groups'
id = Column(Integer, primary_key=True)
name = Column(Unicode(255), unique=True)
class Book(Base):
__tablename__ = 'books'
id = Column(Integer, primary_key=True)
title = Column(Unicode(255))
isbn = Column(Unicode(24))
subjects = relationship('Subject', secondary=subject_books, backref='books')
我还查看了attribute_mapped_collection的文档。但每次我发现每个键只与一个对象关联,而不是与多个对象关联。如果你在任何地方阅读,请提供链接,以便我可以检查它将如何适合你的代码。
我想这对你有帮助。