How to resolve this flask sqlalchemy error "sqlalchemy.exc.InvalidRequestError"? - flask

Question

from datetime import datetime
from pack import db,login_manager
from flask_login import UserMixin
# SQLALCHEMY_TRACK_MODIFICATIONS = False
#login_manager.user_loader
def load_user(user_id):
return User.query.get(int(user_id))
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(20), unique = True, nullable = False)
email = db.Column(db.String(150), unique = True, nullable = False)
password = db.Column(db.String(60), nullable = False)
profile_pic = db.Column(db.String(20), nullable = False, default = "default_profile_pic.jpg")
posts = db.relationship('Post', backref = 'author', lazy = True)
comments = db.relationship('Comment', backref = 'commentor', lazy = True)
def __repr__(self):
return f"User('{self.username}','{self.email}','{self.profile_pic}')"
class Post(db.Model,UserMixin):
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(100), nullable = False)
date_posted = db.Column(db.DateTime, nullable = False, default = datetime.utcnow)
content = db.Column(db.Text, nullable = False)
user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable = False)
post_comments = db.relationship('Comment', backref = 'commentor', lazy = 'dynamic')
def __repr__(self):
return f"Post('{self.title}','{self.content}','{self.date_posted}','{self.comments}')"
class Comment(db.Model):
id = db.Column(db.Integer, primary_key=True)
comment = db.Column(db.String(100000), nullable = False)
timestamp = db.Column(db.DateTime, nullable = False, default = datetime.utcnow, index = True)
user_comment_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable = False)
post_comment_id = db.Column(db.Integer, db.ForeignKey('post.id'))
def __repr__(self):
return f"Post('{self.comment}','{self.user_comment_id}','{self.post_comment_id}')"
This give this error:
sqlalchemy.exc.InvalidRequestError: One or more mappers failed to initialize - can't proceed with initialization of other mappers. Triggering mapper: 'mapped class Post->post'. Original exception was: Error creating backref 'commentor' on relationship 'Post.post_comments': property of that name exists on mapper 'mapped class Comment->comment'
Please help me resolve this error. I want to add a feature to comment on a post and for that i am trying to connect the Comment model with Post and User models.

Answer 1

In your error you have: Post.post_comments': property of that name exists on mapper 'mapped class Comment->comment.
It seems that in User you have comments which creates a backref 'commentor' in Comment and in Post you have post_comments which also creates a backref 'commentor' in Comment.
For example in Post, you can change post_comment to :
post_comments = db.relationship('Comment', backref = 'post_commented', lazy = 'dynamic')
Edit:
When defining a One to Many relationship with backref parameter, there is no need of user_id (in Post), user_comment_id (in Comment), post_comment_id (in Comment): Simply remove them.
You should have another look at https://docs.sqlalchemy.org/en/13/orm/basic_relationships.html#one-to-many (the backref part)