Re: Best way to structure a django project with multiple levels of sub apps?

Once again, I accidently sent this email. Not a fan of the sensitivity of the screen on my new phone. Continued below.

I think if you better define an app vs. a model, you'll find that you need only a few apps.

IMHO, an app should represent a logical segment of your project, broad enough that a majority of the business logic is self-contained and relies little on other apps. Apps should be very high level.

Forgot to mention one exception. I always have a 'common' app that contains all of the models (or views, etc.) used by multiple other applications. In a majority of cases, these are abstract models I use for all of my concrete models in other apps that include fields for auditing such as created_by and created_on. Other examples would include abstract models for addresses, and master views that include logic such as requiring a user be logged in used as mixins for other apps.

In your case, you would likely have apps for 'accounting' and 'engineering', along with other distinct units within the business. The business processes and logic for engineering have little or no overlap with that of accounting. Same with HR, IT, and so on. That's literally as detailed as your apps should be, in which case you'll probably end up with a dozen or so at worst. If it were me, I'd have even less than that with even larger groupings, maybe something along the lines of 'sales' and 'operations' as the only two apps.

One of the key ideas to help understand here is that a Python file containing models does not have to be called models.py. In fact, I usually don't have a models.py at all. Instead, I create a Python module within the app called 'models', which is nothing more than a directory named 'models' that contains __init__.py and all of the Python files that contains my models. Each of those files contains models that are further separated logically. The structure looks like this (some structure omitted for brevity):

business_proj/

    engineering/

        models/

            __init__.py

            abstract_design.py

            abstract_manufacturing.py

            abstract_quality_assurance.py

            design.py

            manufacturing.py

            quality_assurance.py

You could also bury the abstract models in their own module using the same pattern. 

Assuming you have 'engineering' as a registered app, your __init__.py would look

something like this:

from .design import *

from .manufacturing import *

from .quality_assurance import *

This let's Django find all of the models to create the migrations accordingly.

Imports of these models in other locations can also much more objective:

from engineering.models.design import WidgetOutline

In reality, this also works as an alternative because of the __init__.py setup:

from engineering.models import WidgetOutline

But that is slightly less verbose. Your call.

Views and forms (and probably URL's) can be organized using the same pattern. There's no automatic discovery process like models have; views, forms, and URL's can live anywhere with any legal Python name since they are manually imported wherever they are needed. Theoretically your entire project can run inside a single monolithic file.

HTH,

-James

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