Let’s set aside the fact that I think MVC is a horrible design pattern (we’ll talk about that some other day) and focus solely on what happens if you have a standard MVC directory structure:
On the surface it sounds good, right? You put your controllers in the controller folder, the models in the model folder, and so on. This works reasonably well for a small sample application like a blog, since you’ll have maybe 5 controllers, 6 models, and so on.
However, when you you work on a larger application, or you follow the concept of one controller, one action, these number of files in these folders escalates quickly and becomes a tangled mess of naming problems.
Recommended talk: Robert “Uncle Bob” Martin - Architecture: The Lost Years
Let’s look at an example of a social media project. You have Walls, WallPosts, Comments, PrivateConversations, PrivateConversationMessages, and a bunch more stuff. Using a “classic” arrangement, we’ll have quite a sizable directory tree, even without the previously mentioned method:
Now, this is just a simplified example, in your real world application you’ll have a lot more controllers, models and views. If you structure based on what your application is made of (models, views, controllers) your directory structure becomes completely unusable after a certain point.
You can, of course, use the search function of your IDE, but an overloaded directory structure results in the feeling that you have too many classes. This feeling in turn results in a fear of adding new classes, your dev will try to cram a new feature into an existing class even if it does not strictly belong there, resulting in a lot of Single Responsibility Principle violations. Additionally, this structure makes it incredibly hard for a new developer on the team to get a picture of what is what.
Structure based on intent
If we look closely at our controllers, we can draw lines between what belongs together and what doesn’t. For example, from a business perspective the Wall seems to be a concept that is quite clear cut: people can have walls, write posts, and comment on said posts. So let’s put everything related to a wall into one folder. Similarly with private conversations:
Still not great, but better. Now the directory structure can be extended without the fear of too many classes, and if we are looking for something it is quite clear where we can find it.
Before we continue, let’s clarify one thing: these “modules” are not independent. Sometimes they may have cross-dependencies that may need to be addressed if you want to ship the modules separately, but that’s the topic of a different article.
You may notice that now everything within a module is thrown in a single directory. This is good because it will (hopefully) prevent you from adding too many things into one module. However, if you are like me, you still prefer having some structural building blocks around, so let’s bring back the previous directory structure but one level lower:
Small, easy to navigate and easy to read chunks of code. You can, of course, continue adding business structures in a hierarchic fashion as deep as you feel comfortable with. I would advise that you keep it below 3-5 levels to make navigation easy.
Tip: MVC is not suitable to be your overarching design pattern. Instead, I would recommend taking a look at Entity-Boundary-Interactor
To sum it up, your outer most folder structure should be based on business concepts (intents), not the design pattern you chose to use.
Recommended reading: One Controller, One Action