Can't access sqlalchemy database from heroku. Strange error about some 'user' model that I don't have not existing

Question

I have an SQLAlchemy database running on a flask app that works fine locally, but as soon as I run it on Heroku I get a strange issue (See stack trace below).

I don't have a model called 'user' so I don't know what's going on. I've made sure that I've run db.create_all() .

Creating a row in my table works fine, but it's only once I try selecting some rows do I get an issue ( __init__.py ):

@app.route('/blog')
def blog():
    title = 'Blog'
    name = get_name()

    blog_text = []

    for post in sorted(Post.query.filter_by(category=Post.Category.blog),
                       key=lambda p: p.posted_at, reverse=True):
        content = post.content

        blog_text.append(content)

    content = '\n'.join(blog_text)

    return render_template('blog.html', **locals())

And my 'Post' logic in my models.py :

class Post(db.Model):
    __tablename__ = 'user'

    id = db.Column(db.Integer, primary_key=True)

    name = db.Column(db.String(200), nullable=False)
    posted_at = db.Column(db.DateTime, nullable=False, default=datetime.now())
    content = db.Column(db.String(200), nullable=False)
    content_type = db.Column(db.String(200), default="md", nullable=False)  # md / html
    category = db.Column(db.String(200), nullable=False, default="blog")  # poetry / blog

    class Type:
        md = "md"
        html = "html"

    class Category:
        poetry = "poetry"
        blog = "blog"

   ...

Here's the error:

2019-07-12T21:59:09.120100+00:00 app[web.1]: 10.63.22.102 - - [12/Jul/2019:21:59:09 +0000] "GET /blog HTTP/1.1" 500 290 "https://secure-savannah-20745.herokuapp.com/" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36"
2019-07-12T21:59:09.120443+00:00 heroku[router]: at=info method=GET path="/blog" host=secure-savannah-20745.herokuapp.com request_id=c32b2484-c8ff-4910-a4e2-5089eca7c6d3 fwd="98.0.144.26" dyno=web.1 connect=2ms service=66ms status=500 bytes=455 protocol=https
2019-07-12T21:59:13.632588+00:00 app[web.1]: 10.63.22.102 - - [12/Jul/2019:21:59:13 +0000] "GET /projects HTTP/1.1" 200 2342 "https://secure-savannah-20745.herokuapp.com/" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36"
2019-07-12T21:59:13.837771+00:00 app[web.1]: 10.63.22.102 - - [12/Jul/2019:21:59:13 +0000] "GET /static/circles.js HTTP/1.1" 200 0 "https://secure-savannah-20745.herokuapp.com/projects" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36"
2019-07-12T21:59:13.838434+00:00 heroku[router]: at=info method=GET path="/static/circles.js" host=secure-savannah-20745.herokuapp.com request_id=8476c020-fc32-47b3-a4e1-7b6faeb115ca fwd="98.0.144.26" dyno=web.1 connect=1ms service=6ms status=200 bytes=5449 protocol=https
2019-07-12T21:59:13.633394+00:00 heroku[router]: at=info method=GET path="/projects" host=secure-savannah-20745.herokuapp.com request_id=faa3d473-7bda-4e39-810b-e3994eac7390 fwd="98.0.144.26" dyno=web.1 connect=1ms service=1494ms status=200 bytes=2504 protocol=https
2019-07-12T21:59:18.074035+00:00 heroku[router]: at=info method=GET path="/blog" host=secure-savannah-20745.herokuapp.com request_id=e9748e89-dcce-43db-8db8-a16c7fe657ab fwd="98.0.144.26" dyno=web.1 connect=3ms service=12ms status=500 bytes=455 protocol=https
2019-07-12T21:59:18.070372+00:00 app[web.1]: [2019-07-12 21:59:18,069] ERROR in app: Exception on /blog [GET]
2019-07-12T21:59:18.070385+00:00 app[web.1]: Traceback (most recent call last):
2019-07-12T21:59:18.070396+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1244, in _execute_context
2019-07-12T21:59:18.070398+00:00 app[web.1]: cursor, statement, parameters, context
2019-07-12T21:59:18.070403+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 550, in do_execute
2019-07-12T21:59:18.070405+00:00 app[web.1]: cursor.execute(statement, parameters)
2019-07-12T21:59:18.070407+00:00 app[web.1]: sqlite3.OperationalError: no such table: user
2019-07-12T21:59:18.070410+00:00 app[web.1]: 
2019-07-12T21:59:18.070412+00:00 app[web.1]: The above exception was the direct cause of the following exception:
2019-07-12T21:59:18.070414+00:00 app[web.1]: 
2019-07-12T21:59:18.070416+00:00 app[web.1]: Traceback (most recent call last):
2019-07-12T21:59:18.070418+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/flask/app.py", line 2292, in wsgi_app
2019-07-12T21:59:18.070421+00:00 app[web.1]: response = self.full_dispatch_request()
2019-07-12T21:59:18.070423+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/flask/app.py", line 1815, in full_dispatch_request
2019-07-12T21:59:18.070425+00:00 app[web.1]: rv = self.handle_user_exception(e)
2019-07-12T21:59:18.070427+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/flask/app.py", line 1718, in handle_user_exception
2019-07-12T21:59:18.070430+00:00 app[web.1]: reraise(exc_type, exc_value, tb)
2019-07-12T21:59:18.070432+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/flask/_compat.py", line 35, in reraise
2019-07-12T21:59:18.070434+00:00 app[web.1]: raise value
2019-07-12T21:59:18.070436+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/flask/app.py", line 1813, in full_dispatch_request
2019-07-12T21:59:18.070438+00:00 app[web.1]: rv = self.dispatch_request()
2019-07-12T21:59:18.070446+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/flask/app.py", line 1799, in dispatch_request
2019-07-12T21:59:18.070450+00:00 app[web.1]: return self.view_functions[rule.endpoint](**req.view_args)
2019-07-12T21:59:18.070452+00:00 app[web.1]: File "/app/main.py", line 65, in blog
2019-07-12T21:59:18.070455+00:00 app[web.1]: key=lambda p: p.posted_at, reverse=True):
2019-07-12T21:59:18.070457+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 3324, in __iter__
2019-07-12T21:59:18.070459+00:00 app[web.1]: return self._execute_and_instances(context)
2019-07-12T21:59:18.070461+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/orm/query.py", line 3349, in _execute_and_instances
2019-07-12T21:59:18.070463+00:00 app[web.1]: result = conn.execute(querycontext.statement, self._params)
2019-07-12T21:59:18.070466+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 988, in execute
2019-07-12T21:59:18.070468+00:00 app[web.1]: return meth(self, multiparams, params)
2019-07-12T21:59:18.070470+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/sql/elements.py", line 287, in _execute_on_connection
2019-07-12T21:59:18.070472+00:00 app[web.1]: return connection._execute_clauseelement(self, multiparams, params)
2019-07-12T21:59:18.070474+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1107, in _execute_clauseelement
2019-07-12T21:59:18.070477+00:00 app[web.1]: distilled_params,
2019-07-12T21:59:18.070479+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1248, in _execute_context
2019-07-12T21:59:18.070481+00:00 app[web.1]: e, statement, parameters, cursor, context
2019-07-12T21:59:18.070484+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1466, in _handle_dbapi_exception
2019-07-12T21:59:18.070486+00:00 app[web.1]: util.raise_from_cause(sqlalchemy_exception, exc_info)
2019-07-12T21:59:18.070488+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 399, in raise_from_cause
2019-07-12T21:59:18.070491+00:00 app[web.1]: reraise(type(exception), exception, tb=exc_tb, cause=cause)
2019-07-12T21:59:18.070493+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/util/compat.py", line 153, in reraise
2019-07-12T21:59:18.070495+00:00 app[web.1]: raise value.with_traceback(tb)
2019-07-12T21:59:18.070498+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/engine/base.py", line 1244, in _execute_context
2019-07-12T21:59:18.070500+00:00 app[web.1]: cursor, statement, parameters, context
2019-07-12T21:59:18.070502+00:00 app[web.1]: File "/app/.heroku/python/lib/python3.6/site-packages/sqlalchemy/engine/default.py", line 550, in do_execute
2019-07-12T21:59:18.070504+00:00 app[web.1]: cursor.execute(statement, parameters)
2019-07-12T21:59:18.070507+00:00 app[web.1]: sqlalchemy.exc.OperationalError: (sqlite3.OperationalError) no such table: user
2019-07-12T21:59:18.070513+00:00 app[web.1]: [SQL: SELECT user.id AS user_id, user.name AS user_name, user.posted_at AS user_posted_at, user.content AS user_content, user.content_type AS user_content_type, user.category AS user_category
2019-07-12T21:59:18.070515+00:00 app[web.1]: FROM user
2019-07-12T21:59:18.070517+00:00 app[web.1]: WHERE user.category = ?]
2019-07-12T21:59:18.070520+00:00 app[web.1]: [parameters: ('blog',)]
2019-07-12T21:59:18.070661+00:00 app[web.1]: (Background on this error at: http://sqlalche.me/e/e3q8)
2019-07-12T21:59:18.072919+00:00 app[web.1]: 10.63.22.102 - - [12/Jul/2019:21:59:18 +0000] "GET /blog HTTP/1.1" 500 290 "https://secure-savannah-20745.herokuapp.com/projects" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/75.0.3770.100 Safari/537.36"

Answer 1

You missed that your table is named user in your model:

class Post(db.Model):
    __tablename__ = 'user'
    #               ^^^^^^

The reason it doesn't exist is because Heroku doesn't keep your filesystem changes . You are using a SQLite database:

... app[web.1]: sqlite3.OperationalError: no such table: user
#               ^^^^^^^

but a sqlite database is stored on the filesystem of your Heroku dyno. Heroku cleans up ( cycles ) dynos all the time and spins up a new dyno for you for new requests. From their documentation on how Heroku works :

Changes to the filesystem on one dyno are not propagated to other dynos and are not persisted across deploys and dyno restarts. A better and more scalable approach is to use a shared resource such as a database or queue.

Each time a new dyno is spun up to handle your requests, you'll have a new, clean filesystem without your sqlite database, and so an empty database is created again without any tables in it.

Bottom line: You can't use sqlite on Heroku .

Use a Postgres database instead, see the Heroku Postgres documentation . Don't worry, there is a free tier you can use. When you provision the database as an add-on, the DATABASE_URL config var is set for you, which you can read from your app environment.

I usually configure Flask apps that are designed to run on Heroku to read the environment variable but to fall back to a SQLite database when the environment variable is not set:

import os
from pathlib import Path

_project_root = Path(__file__).resolve().parent.parent
_default_sqlite_db = _project_root / "database.db"

SQLALCHEMY_DATABASE_URI = os.environ.get(
    "DATABASE_URL", f"sqlite:///{_default_sqlite_db}"
)

This makes it easy to develop the app locally on SQLite, or set up a local Postgres database for integration testing, and then deploy to Heroku for staging or production.