How to define flask-sqlalchemy objects on demand?

Question

I have a module which I want to use for handling database access to both the production and a test database.

The content looks like this:

class FirstModel(db.Model):
    #...
class SecondModel(db.Model):
    #...

def get_production_connection():
    app = Flask(__name__)
    app.config['SQLALCHEMY_DATABASE_URI'] = PRODUCTION_DATABASE_URI
    db = SQLAlchemy(app)
    return db

def get_test_connection():
    app = Flask(__name__)
    app.config['SQLALCHEMY_DATABASE_URI'] = TEST_DATABASE_URI
    db = SQLAlchemy(app)
    return db

Unfortunately this is not working since the defined models inherit from db.Model which is not defined obviously when the classes are evaluated. Is there any way how I can make the classes/models to inherit from the db.Model class which is only accessible through the db object when one of the methods above is called?

Correct me if I got this wrong: You have an app running in production, and in certain times you'd like to access to production DB, and some times to test DB, right? — cngkaygusuz
– cngkaygusuz, Commented Jun 8, 2014 at 21:50
I'm not familiar with SQLAlchemy, but perhaps you can inherit from SQLAlchemy.Model instead? — Vaughn Cato
– Vaughn Cato, Commented Jun 8, 2014 at 21:55
@cemkyg Sort of: I have some unit tests which should access the test database while the production code should access the production database. I could solve this problem by creating two modules one for production and one for tests within which I create a db object on initialization before all model definitions - but then I would have to define all models twice which is undesirable for me. — ben
– ben, Commented Jun 8, 2014 at 21:55
It seems as if there is no SQLAlchemy.Model - at least in the flask wrapped version I use. — ben
– ben, Commented Jun 8, 2014 at 22:01

ben · Accepted Answer · 2014-06-08 22:07:21Z

2

I solved it now via:

db = SQLAlchemy()

#models here

def create_app():
    app = Flask(__name__)
    #db configuration
    db.init_app(app)
    return db

as shown here http://pythonhosted.org/Flask-SQLAlchemy/api.html#flask.ext.sqlalchemy.SQLAlchemy

answered Jun 8, 2014 at 22:07

ben

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2 Comments

Pedro Werneck Over a year ago

That's correct. Can you accept the answer so this won't pop up in unanswered questions?

ben Over a year ago

Thank you for the hint - accepting my own answer is still blocked for some hours.

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