AttributeError: '_Option' object has no attribute '_sa_instance_state' in flask

Question

I am using Flask for my app and getting AttributeError: '_Option' object has no attribute '_sa_instance_state' error. have no idea what it is about. I google it and it seems that it is a SQL-Alchemy issue. Could you please help me with that?

here is my models.py:

#current table is used to make navigation hierarchy. eg. menu/submenu
#eg. About Us (History, Mission, Vision)
menu_hierarchy = db.Table('menu_hierarchy',
        db.Column('parent_id', db.Integer, db.ForeignKey('menu.id')),
        db.Column('child_id', db.Integer, db.ForeignKey('menu.id'))
    )

class Menu(db.Model):
    """Menu is used for websites navigation titles.
    eg. Home/About Us/Blog/Contacts/and etc""" 

    id          = db.Column(db.Integer, primary_key = True)
    title       = db.Column(db.String(255))
    title_eng   = db.Column(db.String(255))
    alias       = db.Column(db.String(255))
    menu_type   = db.Column(db.String(10))
    ordering    = db.Column(db.SmallInteger, default = '1')
    check_out_time = db.Column(db.DateTime)
    access      = db.Column(db.String(30))
    published   = db.Column(db.SmallInteger, default = '1')
    parent_id   = db.relationship('Menu',
        secondary = menu_hierarchy,
        primaryjoin = (menu_hierarchy.c.parent_id == id),
        secondaryjoin = (menu_hierarchy.c.child_id == id),
        backref = db.backref('menu_hierarchy', lazy = 'dynamic'),
        lazy = 'dynamic')
    content     = db.Column(db.String)
    content_eng = db.Column(db.String)
    image       = db.Column(db.String(350))

Answer 1

It appears the problem is related to an integer (ID) being interpreted as an ORM object.

See this SO post which includes a relevant code sample.