mysql - 如何在 SQLAlchemy 中删除多对一关系中的子项？

Question

首先，我有如下表格:

 class Parent(db.Model):
    __tablename__= "parent"

    id = db.Column("parent_id", db.Integer, primary_key=True)
    childFirst = db.Column(db.Integer, db.ForeignKey('childFirst.childFirst_id'))
    childSecond = db.Column(db.Integer, db.ForeignKey('childSecond.childSecond_id'))
    childThird = db.Column(db.Integer, db.ForeignKey('childThird. childThird_id'))

    child_first = db.relationship("ChildFirst")
    child_second = db.relationship("ChildSecond")
    child_third = db.relationship("ChildThird")

 class ChildFirst(db.Model):
    __tablename__ = "childFirst"

    id = db.Column("childFirst_id", db.Integer, primary_key=True)
    ...

 class ChildSecond(db.Model):
    __tablename__ = "childSecond"

    id = db.Column("childSecond_id", db.Integer, primary_key=True)
    ...

 class ChildThird(db.Model):
    __tablename__ = "childThird"

    id = db.Column("childThird_id", db.Integer, primary_key=True)
    ...

因此，我按照记录建立了多对一关系 here

但是当我尝试删除其中一个 Child 时，出现错误错误:

'Cannot delete or update a parent row: a foreign key constraint fails (`<DB_NAME>`.`<PARENT_NAME>`, CONSTRAINT `<PARENT_NAME>_ibfk_3` FOREIGN KEY (`<CHILD_ID_COLUMN>`) REFERENCES `<CHILD_TABLE_NAME>` (`<CHILD_ID_COLUMN>`))')
[SQL: DELETE FROM CHILD_TABLE_NAME WHERE <CHILD_TABLE_NAME>.<CHILD_ID_COLUMN> = %(<CHILD_ID_COLUMN>_1)s]

实际上我正在尝试使用此命令删除子项 -> CHILD_CLASS.query.filter_by(id=<id_variable>).delete()

最后，我使用的是mysql数据库。

那么，出了什么问题？

谢谢并致以诚挚的问候..

Answer 1

当我删除子行时，我删除成功。

代码:

child = <CHILD_CLASS>.query.filter_by(id=<id>).first()
db.session.delete(child)
db.session.commit()

但是有什么区别呢？