Question

我有一个班级Revision，Revision有以下定义：

class Revision(db.Model):
    id = db.Column(db.Unicode, primary_key=True)
    text = db.Column(db.Unicode)

此外，每个Revision 可以拥有一个祖先，就像与另一个Revision的关系一样。每个Revision也应该跟踪任何后继者，即Revision，它将它作为他们的祖先。我尝试了以下两种方法：

ancestorId = db.Column(db.Unicode, db.ForeignKey("revision.id"))
successors = db.relationship("Revision", backref="ancestor", lazy="dynamic")

投掷：

sqlalchemy.exc.ArgumentError: Revision.successors and back-reference Revision.ancestor are both of the same direction <symbol 'ONETOMANY>.  Did you mean to set remote_side on the many-to-one side ?

和

successors = db.relationship("Revision", backref="ancestor", lazy="dynamic")

投掷：

sqlalchemy.exc.ArgumentError: Could not determine join condition between parent/child tables on relationship Revision.successors.  Specify a 'primaryjoin' expression.  If 'secondary' is present, 'secondaryjoin' is needed as well.

Answer 1

您想要的是adjacency list。 SQLAlchemy在其examples目录中有一个example。重要的部分是backref的remote_side参数：

ancestorId = db.Column(db.Unicode, db.ForeignKey(id))
successors = db.relationship("Revision",
                             backref=db.backref("ancestor", remote_side=id),
                             lazy="dynamic")

将一个类与自身联系起来

1 个答案: