Flask database ProductsUser UniqueConstraint configuration not work.

[HankDa]

in flask main.py

class ProductsUser(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    user_id = db.Column(db.Integer)
    product_id = db.Column(db.Integer)
    # TODO: not working actually
    UniqueConstraint('user_id', 'product_id', name='user_product_unique')

where

UniqueConstraint('user_id', 'product_id', name='user_product_unique')

user_id and product_id should be instance instead of string, modified code to :

UniqueConstraint(user_id, product_id, name='user_product_unique')

then migrate database again that fixed this issue.