提交后 Flask-SQLAlchemy 多对多邻接列表更改

Question

我有一个与自身具有多对多关系的模型：一个操作可以被另一个操作或自身阻止。

operation_to_operation_association_table = db.Table(
    "preventing_operations",
    db.Column("id", db.Integer, primary_key=True),
    db.Column("preventing_operation_id", db.Integer, db.ForeignKey("operation.id")),
    db.Column("prevents_operation_id", db.Integer, db.ForeignKey("operation.id")))



class Operation(BaseModel): # BaseModel defines id and creation/update times
    name = db.Column(db.String)

    bodypart_id = db.Column(db.Integer, db.ForeignKey(BodyPart.id))
    bodypart = db.relationship("BodyPart", backref="operations")

    prevents = db.relationship("Operation", secondary=operation_to_operation_association_table,
                               foreign_keys=[operation_to_operation_association_table.c.preventing_operation_id],
                               backref="prevented_by")


    def __eq__(self, other):
        return other and self.name == other.name and self.bodypart == other.bodypart

然后在 shell 中，来自一个新的数据库：

In [1]: bp = BodyPart(name="liver")

In [2]: db.session.add(bp)

In [3]: db.session.commit()

In [4]: o1, o2 = Operation(name="viewing", bodypart=bp), Operation(name="removing", bodypart=bp)

In [5]: db.session.add_all([o1, o2])

In [6]: db.session.commit()

In [7]: o1, o2
Out[7]: (Viewing the liver (1), Removing the liver (2))

In [8]: o1.prevents, o2.prevents
Out[8]: ([], [])

In [9]: o2.prevents.append(o1)

In [10]: o1.prevents, o2.prevents
Out[10]: ([], [Viewing the liver (1)])

In [11]: db.session.commit()

In [12]: o1.prevents, o2.prevents
Out[12]: ([Viewing the liver (1)], [])

提交会切换列表？！

记录查询，SQLAlchemy 发送数据库的插入查询好像是错误的：

INSERT INTO preventing_operations (prevents_operation_id) VALUES (?)
with values (1,)

应该是：

INSERT INTO preventing_operations (prevents_operation_id, preventing_operation_id) VALUES (?)
with values (2, 1)

我在这里做错了什么？我是否错误地定义了我的关系？那为什么它只在我提交时才改变？

Answer 1

问题出在 foreign_keys 设置上，我实际上不确定 foreign_keys 到底需要做什么。

但我建议改用primaryjoin和secondaryjoin。这样设置对我来说更明显（并且有效）：

prevents = relationship(
    "Operation",
    secondary=operation_to_operation,
    primaryjoin=id == operation_to_operation.c.preventing_operation_id,
    secondaryjoin=id == operation_to_operation.c.prevents_operation_id,
    backref="prevented_by")

这里是the working example and module with base model.

运行示例如下： - 下载这两个文件，保存到同一个文件夹中（或克隆 repo） - 运行`pythonmany_many_save_issue.py。

我用 SQLAlchemy==1.0.6 测试过。

提交后 Flask-SQLAlchemy 多对多邻接列表更改

Flask-SQLAlchemy many-to-many adjacency list changes after commit

python

sqlalchemy

adjacency-list

flask

flask-sqlalchemy