Question

我认为我和here on SO.使用python 3.5，flask-sqlalchemy和sqlite有同样的问题。我正在尝试建立一个（用户）到多个（后）关系。

class User(db_blog.Model):
    id = db_blog.Column(db_blog.Integer, primary_key=True)
    nickname = db_blog.Column(db_blog.String(64), index=True, unique=True)
    email = db_blog.Column(db_blog.String(120), unique=True)
    posts = db_blog.relationship('Post', backref='author', lazy='dynamic')

    def __repr__(self):
        return '<User: {0}>'.format(self.nickname)

class Post(db_blog.Model):
    id = db_blog.Column(db_blog.Integer, primary_key=True)
    body = db_blog.Column(db_blog.String(2500))
    title = db_blog.Column(db_blog.String(140))
    user_id = db_blog.Column(db_blog.Integer, db_blog.ForeignKey('user.id'))

    def __init__(self, body, title, **kwargs):
        self.body = body
        self.title = title

    def __repr__(self):
        return '<Title: {0}\nPost: {1}\nAuthor: {2}>'.format(self.title, self.body, self.author)

作者是无。

>>> u = User(nickname="John Doe", email="jdoe@email.com")
>>> u
<User: John Doe>
>>> db_blog.session.add(u)
>>> db_blog.session.commit()
>>> u = User.query.get(1)
>>> u
<User: John Doe>
>>> p = Post(body="Body of post", title="Title of Post", author=u)
>>> p
<Title: Title of Post
Post: Body of post
Author: None> #Here I expect- "Author: John Doe>"

我在帖子的会话添加/提交后得到相同的结果，因此无法找到帖子作者。

Answer 1

如果您将新创建的post添加到用户的posts属性，它将起作用：

>>> u = User(nickname="John Doe", email="jdoe@email.com")
>>> u
<User: John Doe>
>>> db_blog.session.add(u)
>>> p = Post(body="Body of post", title="Title of Post")
>>> p
<Title: Title of Post
Post: Body of post
Author: None>
>>> db_blog.session.add(p)
>>> db_blog.session.commit()
>>> u.posts.append(p)
>>> p
<Title: Title of Post
Post: Body of post
Author: <User: John Doe>>
>>> p.author
<User: John Doe>

您的代码无法正常工作的原因，是因为您为__init__类定义了Post构造函数，而这并不考虑author字段所有，所以Python不知道如何处理author参数。

Answer 2

您已将自己的__init__添加到Post。虽然它接受关键字参数，但它对它们没有任何作用。您可以更新它以使用它们

def __init__(self, body, title, **kwargs):
    self.body = body 
    self.title = title
    for k, v in kwargs:
        setattr(self, k, v)

或者，理想情况下，您可以删除该方法并让SQLAlchemy为您处理它。

Flask-SQLAlchemy - Backref不起作用，值为None

2 个答案: