Flask and SQLAlchemy, application not registered on instance

Question

I\'m currently trying to piece together a small Flask application. This is my structure.

run.py
application
  __init__.py
  database.py
  models.py
  views.p         


        

Answer 1

The answer is here: http://flask-sqlalchemy.pocoo.org/latest/api/#configuration

See the part about:

The difference between the two is that in the first case methods like create_all() and drop_all() will work all the time but in the second case a flask.Flask.request_context() has to exist.

There's more information here: http://flask-sqlalchemy.pocoo.org/latest/contexts/

If all that is confusing (it probably is, since it's talking about a fairly advanced feature of Flask), the short short version is db.init_app(app) changes the app object, but it doesn't change anything in the db object. It's on purpose because there might be more than one app flying around, and db might have to talk to all of them. (I said it was an advanced feature.)

So when you call db.create_all() without having a request live (which creates a global that has the currently running app) it doesn't know what to connect to, and bombs. That's what the error means.

In your case, I would put the SQLAlchemy call back in __init__.py and pass app to it, that's the easiest way:

db = SQLAlchemy(app)

Or keep things as they are, and run the setup before the first request:

@app.before_first_request
def create_database():
     db.create_all()

I hope that helps! Let me know if you run into any more problems.