(Flask) Heroku Error: sqlalchemy.exc.ProgrammingError: (psycopg2.errors.DuplicateTable) relation "user" already exists

Question

I want to update my database tables in heroku. However, when I check the status of my tables using heroku pg:info DATABASE , I realize there are no tables created, yet they are defined in models.py as seen at the bottom of the question.

=== DATABASE_URL
Plan:                  Hobby-dev
Status:                Available
Connections:           0/20
PG Version:            12.4
Created:               2020-10-13 23:10 UTC
Data Size:             8.2 MB
Tables:                0 # <---------------------------no tables
Rows:                  0/10000 (In compliance)
Fork/Follow:           Unsupported
Rollback:              Unsupported
Continuous Protection: Off
Add-on:                postgresql-closed-00235

This is how my Python Flask app is set up:

config.py

import os

basedir = os.path.abspath(os.path.dirname(__file__))

class Config(object):
    SECRET_KEY = os.environ.get('SECRET_KEY') or 'you-will-never-guess'
    SQLALCHEMY_DATABASE_URI = os.environ.get('DATABASE_URL') or \
        'sqlite:///' + os.path.join(basedir, 'app.db')
    SQLALCHEMY_TRACK_MODIFICATIONS = False

    MAIL_SERVER='smtp.gmail.com'
    MAIL_PORT=587
    MAIL_USE_TLS=1
    MAIL_USERNAME='my-username'
    MAIL_PASSWORD='my-password'
    ADMINS=['admin-email']

    POSTS_PER_PAGE=10

    STRIPE_PUBLISHABLE_KEY='<stripe-publishable-key>'
    STRIPE_SECRET_KEY='<stripe-secret-key>'
    STRIPE_ENDPOINT_SECRET='<stripe-endpoint-secret>'

    LOG_TO_STDOUT = os.environ.get('LOG_TO_STDOUT')

__init__.py

from flask import Flask
from config import Config
from flask_bootstrap import Bootstrap
from flask_sqlalchemy import SQLAlchemy
from flask_migrate import Migrate
from flask_login import LoginManager
import logging
from logging.handlers import SMTPHandler, RotatingFileHandler
import os
from flask_mail import Mail
from flask_moment import Moment
import stripe

app = Flask(__name__)
app.config.from_object(Config)
db = SQLAlchemy(app)
migrate = Migrate(app, db)
login = LoginManager(app)
login.login_view = 'login'
bootstrap = Bootstrap(app)
mail = Mail(app)
moment = Moment(app)

stripe_keys = {
    'secret_key': app.config['STRIPE_SECRET_KEY'],
    'publishable_key': app.config['STRIPE_PUBLISHABLE_KEY'],
    'endpoint_secret': app.config['STRIPE_ENDPOINT_SECRET']
}
stripe.api_key = stripe_keys['secret_key']

if not app.debug:
    if app.config['MAIL_SERVER']:
        auth = None
        if app.config['MAIL_USERNAME'] or app.config['MAIL_PASSWORD']:
            auth = (app.config['MAIL_USERNAME'], app.config['MAIL_PASSWORD'])
        secure = None
        if app.config['MAIL_USE_TLS']:
            secure = ()
        mailhandler = SMTPHandler(            
            mailhost=(app.config['MAIL_SERVER'], app.config['MAIL_PORT']),
            fromaddr='noreply@' + app.config['MAIL_SERVER'],
            toaddrs=app.config['ADMINS'],
            subject='Somasoma: Error',
            credentials=auth, secure=secure
        )
        mailhandler.setLevel(logging.ERROR)
        app.logger.addHandler(mailhandler)
    if app.config['LOG_TO_STDOUT']:
        stream_handler = logging.StreamHandler()
        stream_handler.setLevel(logging.INFO)
        app.logger.addHandler(stream_handler)
    else:
        if not os.path.exists('logs'):
            os.mkdir('logs')
        file_handler = RotatingFileHandler('logs/somasoma.log', maxBytes=10240, backupCount=10)
        file_handler.setFormatter(logging.Formatter(
            '%(asctime)s %(levelname)s: %(message)s [in %(pathname)s:%(lineno)d] '
        ))
        file_handler.setLevel(logging.INFO)
        app.logger.addHandler(file_handler)

    app.logger.setLevel(logging.INFO)
    app.logger.info('Somasoma Blog')

from app import routes, models, errors

blog_app.py

from app import app, db
from app.models import User, Post

@app.shell_context_processor
def make_shell_context():
    return {'db':db, 'User': User, 'Post': Post}

Procfile

web: flask db upgrade; gunicorn blog_app:app

Ideally, to update my database, I have run heroku run flask db upgrade command. This instead throws me this error:

sqlalchemy.exc.ProgrammingError: (psycopg2.errors.DuplicateTable) relation "user" already exists

[SQL: 
CREATE TABLE "user" (
        id SERIAL NOT NULL, 
        username VARCHAR(64), 
        email VARCHAR(120), 
        password_hash VARCHAR(128), 
        about_me VARCHAR(140), 
        last_seen TIMESTAMP WITHOUT TIME ZONE, 
        PRIMARY KEY (id)
)

The thing is when I try to log into my deployed up on heroku, I cannot sign up or sign in because of non-existent 'user' as seen in the stdout heroku log:

psycopg2.errors.UndefinedTable: relation "user" does not exist
2020-10-13T23:27:13.018103+00:00 app[web.1]: LINE 2: FROM "user"

SQL: SELECT "user".id AS user_id, "user".username AS user_username, "user".email AS user_email, "user".password_hash AS user_password_hash
2020-10-13T23:27:13.018113+00:00 app[web.1]: FROM "user"
2020-10-13T23:27:13.018114+00:00 app[web.1]: WHERE "user".username = %(username_1)s
2020-10-13T23:27:13.018114+00:00 app[web.1]: LIMIT %(param_1)s]
2020-10-13T23:27:13.018114+00:00 app[web.1]: [parameters: {'username_1': 'harry', 'param_1': 1}]
2020-10-13T23:27:13.018114+00:00 app[web.1]: (Background on this error at: http://sqlalche.me/e/f405)

This error is a direct result of the database tables being empty. I have looked at several example solutions such as this and this but I am not quite able to solve the database issue I am facing.

Personally, I thought that the inclusion of the argument db while instantiating the migrate variable in __init__.py would solve that. I mean:

Instead of:

migrate = Migrate(app)

Then this should fix it:

migrate = Migrate(app, db)

However, with that addition, I am still not able to fix this error.

What could I be missing out on? Any lead or direction is much appreciated.

Edited :

I have a user and post model defined for my database: models.py

class User(UserMixin, db.Model):
    id = db.Column(db.Integer, primary_key = True)
    username = db.Column(db.String(64), index = True, unique = True)
    email = db.Column(db.String(120), index =  True, unique = True)
    password_hash = db.Column(db.String(128))

    posts = db.relationship('Post', backref = 'author', lazy = 'dynamic')

    def __repr__(self):
        return '<User {}>'.format(self.username)   

class Post(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    body = db.Column(db.String(140))
    timestamp = db.Column(db.DateTime, index = True, default = datetime.utcnow)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'))

    def __repr__(self):
        return 'Post <>'.format(self.body)

@login.user_loader
def load_user(id):
    return User.query.get(int(id))

Answer 1

This happened because you have dropped the alembic_version table. It can be rectified in your project's Procfile . Open your Procfile , copy and paste this code snippet:

release: flask db upgrade
release: flask db stamp head

web: gunicorn app:app