AttributeError: ‘ int’对象没有属性‘_sa_instance_state’

我正在使用 Flask 开发论坛模板。当我尝试使用表单在浏览器中创建新线程时，SQLAlchemy 将引发 AttributeError。当我尝试使用 Forum-to-Thread 实现一对多关系和使用 Thread-to-User 实现一对多关系时，出现了这个问题。

Models.py

class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(32), index=True, unique=True)
password = db.Column(db.String(32), index=True)
email = db.Column(db.String(120), index=True, unique=True)
role = db.Column(db.SmallInteger, default=ROLE_USER)


posts = db.relationship('Post', backref='author', lazy='dynamic')


class Forum(db.Model):
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(128))
description = db.Column(db.Text)


threads = db.relationship('Thread', backref='forum', lazy='dynamic')


class Thread(db.Model):


id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(128))
author= db.Column(db.String(32))
timestamp = db.Column(db.DateTime)
forum_id = db.Column(db.Integer, db.ForeignKey('forum.id'))


posts = db.relationship('Post', backref='thread', lazy='dynamic')


class Post(db.Model):


id = db.Column(db.Integer, primary_key=True)
body = db.Column(db.Text)
timestamp = db.Column(db.DateTime)
thread_id = db.Column(db.Integer, db.ForeignKey('thread.id'))
user_id = db.Column(db.Integer, db.ForeignKey('user.id'))

在 views.py 中处理的所有新文章/线程

视野，视野

@app.route('/forum/id=<id>/submit', methods=['GET','POST'])
@login_required
def new_thread(id):
form = ThreadForm()
forum = Forum.query.filter_by(id=id).first()
if form.validate_on_submit():
thread = Thread(title=form.title.data,
author=g.user.username,
timestamp=datetime.utcnow())
db.session.add(thread)
db.session.flush()
post = Post(body=form.body.data,
timestamp=datetime.utcnow(),
thread=thread.id,
author=g.user.id)
db.session.add(post)
db.session.commit()
flash('Post successful.')
return redirect(url_for('forum_index', id=id))
return render_template('forum/thread_submit.html', title=forum.title, form=form)