Calling flask app configuration inside models.py

Question

OK, I am trying to do something a little bit esoteric with my Flask application.

I want to have some conditional logic in the model structure that is based on information in a configuration file.

At present when I call my Flask App, a configuration object is specified like this:

app = create_app('swarm.settings.DevConfig')

The db object is created in the models.py :

from flask_sqlalchemy import SQLAlchemy

db = SQLAlchemy()

class MyClass(db.Model):
    ...

I would like the models.py to accommodate a variety of ORM and OGM (not limited to SQLAlchemy and py2neo) so that I can develop a Flask app to be SQL/Graph agnostic.

if __SOME_CONFIG__['db_mapper'] = 'SQLAlchemy':
    from flask_sqlalchemy import SQLAlchemy
    db = SQLAlchemy()
    class MapperModel(db.Model):
        ...
elif __SOME_CONFIG__['db_mapper'] = 'Py2Neo':

    from py2neo import Graph, Node, Relation
    db = Graph()
    class MapperModel(py2neo.Node):
        ...

class MyClass(MapperModel):
    ...

I can't see a way to use current_app to achieve this because I am creating my db object before the code is aware of an app object.

Is there a simple way to load the current configuration object from inside models.py ? Should I just load the configuration in models.py from a seperate file in the without reference to the app's current configuration object?

score 1 · Answer 1 · answered Mar 08 '17 at 09:23

1

Create a function which will return a db object, and initialize this object when you instantiate flask application:

app = create_app(...)
db = create_dbobject('someconfig')

def create_dbobject(someconfig):
    if someconfig == 'Py2Neo':
        return Py2Neo()
    #default to sqlchemy
    return SQLAlchemy()

So no more you have to worry about extension initialization. And its good to keep extensions initialization in place where app exists.

answered Mar 08 '17 at 09:23

metmirr

4,234
2
21
34

Where do you suggest putting that piece of code? If I put it inside the `__init__.py` file, whenever I try to import from the package, the `app` and `db` objects get assigned automatically and it becomes a mess. Is there any way to handle this? – Kevin Jul 18 '18 at 05:32
You can still put it in the `__init__.py` file as `create_dbobject` function and in the `create_app` function call `create_dbobject` function to get db instance. But outside of the `create_app` function define `db = SQLAlchemy() # this is default ` in `create_app` function you can reassign it to Graph instance. Hence db instance is global and generic to your config you can use it without error. – metmirr Jul 18 '18 at 08:52
Makes sense. Any reason why you would want to assign the db outside? A better way would be to define `db = SQLAlchemy()` inside any file that needs it instead of importing it from the `__init__.py` file, no? – Kevin Jul 18 '18 at 09:57
This approach is good if you have sqlalchemy and graph as flask extensions. And you might want to use db instance from the shell. – metmirr Jul 18 '18 at 12:10

Calling flask app configuration inside models.py

1 Answers1