AttributeError: 'int' object has no attribute '_sa_instance_state'

Question

I'm working on forum template using Flask. When I attempt creating a new thread in the browser using forms, SQLAlchemy throws an AttributeError. The problem showed up when I tried implementing a one-to-many relationship with Forum-to-Thread and a one-to-many relationship with Thread-to-User.

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')) 

All the new posts/threads and handled within views.py

views.py

@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)  

Answer 1

the problem is this:

post = Post(body=form.body.data,             timestamp=datetime.utcnow(),             thread=thread.id,             author=g.user.id) 

you want to work with ORM objects, not primary key columns:

post = Post(body=form.body.data,             timestamp=datetime.utcnow(),             thread=thread,             author=g.user) 

the error means that an integer is being interpreted as an ORM object.