Alembic / Flask-migrate migration on Heroku runs but does not create tables

Question

I am attempting to deploy a Flask app to Heroku. I have pushed to Heroku and can access my login page but any call to the db gives an OperationalError:

2014-01-29T12:12:31.801772+00:00 app[web.1]: OperationalError: (OperationalError) no such table: projects_project u'SELECT

Using Flask-migrate I can successfully run local migrations and upgrades:

INFO  [alembic.migration] Context impl PostgresqlImpl.
INFO  [alembic.migration] Will assume transactional DDL.
INFO  [alembic.migration] Running upgrade None -> 4b56d58e1d4c, empty message

When I try to upgrade on Heroku using heroku run python manage.py db upgrade the upgrade appears to happen, but the Context impl. is now SQLite?:

(dev01)Toms-MacBook-Pro:dev01 kt$ heroku run python manage.py db upgrade
Running `python manage.py db upgrade` attached to terminal... up, run.9069 
INFO  [alembic.migration] Context impl SQLiteImpl.
INFO  [alembic.migration] Will assume non-transactional DDL.
INFO  [alembic.migration] Running upgrade None -> 4b56d58e1d4c, empty message

Running Heroku pg:info gives:

=== HEROKU_POSTGRESQL_PINK_URL (DATABASE_URL)
Plan:        Dev
Status:      available
Connections: 0
PG Version:  9.3.2
Created:     2014-01-27 18:55 UTC
Data Size:   6.4 MB
Tables:      0
Rows:        0/10000 (In compliance)
Fork/Follow: Unsupported
Rollback:    Unsupported

The relevant logs for the Heroku upgrade are:

2014-01-29T12:55:40.112436+00:00 heroku[api]: Starting process with command `python manage.py db upgrade` by kt@gmail.com
2014-01-29T12:55:44.638957+00:00 heroku[run.9069]: Awaiting client
2014-01-29T12:55:44.667692+00:00 heroku[run.9069]: Starting process with command `python manage.py db upgrade`
2014-01-29T12:55:44.836337+00:00 heroku[run.9069]: State changed from starting to up
2014-01-29T12:55:46.643857+00:00 heroku[run.9069]: Process exited with status 0
2014-01-29T12:55:46.656134+00:00 heroku[run.9069]: State changed from up to complete

Also, heroku config gives me:

(dev01)Toms-MacBook-Pro:dev01 kt$ heroku config
=== myapp Config Vars
DATABASE_URL:               postgres://xxx.compute-1.amazonaws.com:5432/da0jtkatk6057v
HEROKU_POSTGRESQL_PINK_URL: postgres://xxx.compute-1.amazonaws.com:5432/da0jtkatk6057v

where [xxx == xxx]

How is the Context impl. set? Apart from this obvious difference between working local and heroku, I can't work out what's happening or how I should debug. Thanks.

Answer 1

The URL for the database is taken from the SQLALCHEMY_DATABASE_URI configuration in your Flask app instance. This happens in the env.py configuration for Alembic that was created in the migrations folder.

Are you storing the value of os.environ['DATABASE_URL'] in the configuration before you hand over control to Flask-Migrate and Alembic? It seems you have a default SQLite based database that never gets overwritten with the real one provided by Heroku.