Table 'roles_users' is already defined for this MetaData instance

Question

I'm trying to get a current_user information in my views and I include from users.models import *

Then in my code return current_user;

@app.route('/panel')
@login_required
def access_panel():
    return current_user.email;

Once I run my server it says:

Traceback (most recent call last):
  File "manage.py", line 6, in <module>
    from nadel import app
  File "/Users/tbd/Desktop/Projects/nadel/__init__.py", line 27, in <module>
    from users import views
  File "/Users/tbd/Desktop/Projects/nadel/users/views.py", line 5, in <module>
    from users.models import *
  File "/Users/tbd/Desktop/Projects/nadel/users/models.py", line 8, in <module>
    db.Column('role_id', db.Integer(), db.ForeignKey('role.id')))
  File "/Library/Python/2.7/site-packages/flask_sqlalchemy/__init__.py", line 67, in _make_table
    return sqlalchemy.Table(*args, **kwargs)
  File "/Library/Python/2.7/site-packages/sqlalchemy/sql/schema.py", line 398, in __new__
    "existing Table object." % key)
sqlalchemy.exc.InvalidRequestError: Table 'roles_users' is already defined for this MetaData instance.  Specify 'extend_existing=True' to redefine options and columns on an existing Table object.

In my model I have:

from nadel import db
from flask.ext.security import UserMixin, RoleMixin

# Define models
roles_users = db.Table('roles_users',
        db.Column('user_id', db.Integer(), db.ForeignKey('user.id')),
        db.Column('role_id', db.Integer(), db.ForeignKey('role.id')))

class Role(db.Model, RoleMixin):
    id = db.Column(db.Integer(), primary_key=True)
    name = db.Column(db.String(80), unique=True)
    description = db.Column(db.String(255))

class User(db.Model, UserMixin):
    id = db.Column(db.Integer, primary_key=True)
    email = db.Column(db.String(255), unique=True)
    name = db.Column(db.String(255))
    password = db.Column(db.String(255))
    active = db.Column(db.Boolean())
    #confirmed_at = db.Column(db.DateTime())
    last_login_at = db.Column(db.DateTime())
    current_login_at = db.Column(db.DateTime())
    last_login_ip = db.Column(db.String(32))
    current_login_ip = db.Column(db.String(32))
    login_count = db.Column(db.Integer)

    roles = db.relationship('Role', secondary=roles_users,
                            backref=db.backref('users', lazy='dynamic'))

I don't understand why I am getting this error and how to solve it.

Answer 1

Try adding:

__table_args__ = {'extend_existing': True}

right below __tablename__

Reference: https://docs.sqlalchemy.org/en/13/orm/extensions/declarative/table_config.html?highlight=table_args

Answer 2

I had a similar error. My problem was importing the class that inherits db.Model from two different files using a relative import. Flask-SQLAlchemy mapped the two imports as two different table definitions and tried to create two tables. I fixed this issue by using the absolute import path in both files.

Answer 3

I had this error when I had created a new class by copy-pasting a previous class. It turned out I had forgotten to change the __tablename__, so I had two classes with the same __tablename__ property. This caused the error, and changing the property resolved it.