[英]Flask + SQLAlchemy adjacency list backref error
I have the following model: 我有以下型号:
class Category(db.Model):
__tablename__ = 'categories'
id = db.Column(db.Integer, primary_key=True)
parent_id = db.Column(db.Integer, db.ForeignKey(id), nullable=True)
level = db.Column(db.SmallInteger)
name = db.Column(db.String(200))
children = db.relationship('Category', backref=backref('parent', remote_side=id))
def __repr__(self):
return '<Category %r>' % (self.name)
This doesn't seem to work. 这似乎不起作用。 I always get the following error:
我总是得到以下错误:
NameError: name 'backref' is not defined
What am I doing wrong? 我究竟做错了什么?
On this line... 在这条线上......
children = db.relationship('Category', backref=backref('parent', remote_side=id))
You are using the attribute backref
, but have never defined it. 您正在使用
backref
属性,但从未定义过它。 You would get a similar error if you had wrote... 如果你写了......你会得到类似的错误
children = db.relationship('Category', backref=photosynthesis('parent', remote_side=id))
Same problem: Python doesn't know what "photosynthesis" is. 同样的问题:Python不知道“光合作用”是什么。
So, what is backref actually supposed to be in your code? 那么,什么是backref实际上应该在你的代码中呢? Turns out it's a function that is part of SQLAlchemy .
原来它是SQLAlchemy的一部分功能 。 Like many of these functions (eg, the "relationship" function you are using), Flask-SQLAlchemy will provide to you an alias so you don't need to import them directly.
与许多这些函数(例如,您正在使用的“关系”函数)一样,Flask-SQLAlchemy将为您提供别名,因此您无需直接导入它们。
You can use the docs as your guide. 您可以使用文档作为指南。 Instead of
backref=backref
, you want backref=db.backref
. 而不是
backref=backref
,你想要backref=db.backref
。
You have to explicit what backref is. 你必须明确backref是什么。 You can do it with this import:
您可以使用此导入执行此操作:
from sqlalchemy.orm import backref
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