Django project applications division

Question

I'm currently writing django project and got confused when it came to separation into apps. Project consists of posts and categories which are kept in one app, also there is a 'main' app which handles user profile view, login, logout and registration. Now I'm trying to implement user-to-user messages and I'm wondering if it should be kept as separate app.

If Message model is kept in application 'messages' how do I realize show_messages view?

1) It seems that it should be stored in 'main' app since it's linked by my_profile view. It would just get all Message instances form 'messages' app and render template extending profile.html or including from 'messages' app a partial template responsible only for messages listing. But why would I then need separate application just to hold one model there with some helper functions?

2) Secondly I wonder about placing show_messages view in 'messages' app but then I would need to use template which extends template from other application which again seems to be violation of self-containment rule. Also all "accounts/" urls are currently kept in main.urls so I feel wrong about adding "accounts/profile/messages" rule to messages.url.

3) Finally I think about moving Message model with all helpers and templates to 'main' app since messages are designed to work with User models and views therefore forcing additional separation seems useless.

Thanks for reading my thoughts, I'll appreciate all clues and explanations.

Answer 1

When I first started working with Django, I found the answers on this SO question to be particularly helpful, regarding app/project layout: Projects vs Apps

Many of the answers are useful, but this one is particularly pithy:

Try to answer question: "What does my application do?". If you cannot answer in single sentence, then maybe you can split it to several apps with cleaner logic?

I've read this thought somewhere soon after I've stared to work with django and I find that I ask this question my self quite often and it helps me.

Your apps don't have to be reusable, they can depend on each other, but they should do one thing.

Interdependence of apps isn't always problematic. For example, in a lot of my projects I have a separate app that is used solely for creating dynamic menus. In order to work properly, I need to import the specific models of that site into that app -- so I couldn't just drop it into another site, unaltered, and expected it to work. Nonetheless, the other 90% of the code in that app is completely reusable, and it's easier for me to move the relevant code to a new project if its already spun out into a separate app -- even though that app only holds a templatetag and a template.

Ultimately, a django site would technically run just fine with ALL models/views/etc in one big, unwieldy app. But by breaking your project down into "this app performs this specific function" you're probably going make managing your code a lot easier for yourself.

Regarding the 'url' point in 2, there's no reason not to subspace URLs. You are already doing this in a django project already -- mostly likely your main urls.py has an include() to another app, such as your main.urls. There's no reason your main.urls can't also have an include() to your messages app.