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How to keep business logic out of the views in django?

If you look around, you'll find many references telling you to keep your business logic out of your views. This seems reasonable and by providing an example, those resources will explain this in a way that it makes total sense, at least at the time. Sadly, since your project is probably very different than the example, once you want to organize your code, you start having some doubts and you have no idea where to put everything.

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The next time you want to split that 200 lines view function, start by identifying the main logic blocks of the function. Stuff like: fetching the data from the database, validating inputs from the users (never thrust them!), formatting data before rendering it, ...

If you have trouble identifying the blocks, think about how would you write tests to validate those blocks in a simple way. By doing so, your logic will tend to become simpler and more composable.

Now for each block you identified:

  • If the logic of the block is applied to a single instance of an single model, then it should be a method or attribute directly on that model;

  • If the logic is applied to more than instance of a single model, also known as queryset, keep it in a model manager;

  • If it applies to different models (or none), store the business logic into a file called services.py or helpers.py in the appropriate app;

  • If it applies different models (or none) of different apps, store it in a services.py/helpers.py in the project's root. You can also create an separate app to store business logic that touches more than app at once.

Instead of providing some example, in providing this "reasoning" guide, I hope you can apply this more easily to your project.

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