has_many :through model names, controller and attributes best practices?

Question

Disclaimer: I really spent time thinking about names of models and variables. If you also do, this question is for you.

I have a Rails project which contains two models: User and Project.

They are connected by the model ProjectsUser, which is a connection model in a many-to-many relationship. This model also holds the role of a user in the given project, along with other attributes such as tier and departments. So this is a has_many :through relationship.

Given this scenario, here is everything that always bothered me on all my rails projects since I started developing on it:

1. Should I use a ProjectsUserController or better add the relevant actions on UserController and ProjectController? At some point, I want to assign users to a project, or even changing the role of a user in a given project. Is it a better practice to leave those actions on the connection controller, or use the model controllers?

2. Should I write a method to get the role of a user for a given project? This is basically if I should have a method User#role_for(project) or not. Since this method basically is getting the information from the projects_user object it could make more sense to always let this explicity on the code, since most of the times I'll have the project and the user, but not the projects_user. Is this line of thinking correct, or maybe the problem is that I'm should have more project_user on my code than I really do? Are there good caveats for this?

3. Should I try to rename my table to a non-standard name if it is not obvious? Ok, I got that if I have the models User and NewsSite I should use has_many :subscriptions, but the thing is that naming those models in real life cases are usually harder, by my experience. When the name ends up not being that obvious (for exemple, in my case, maybe project_participation as @wonderingtomato suggested) is for the best, or in those cases it is better to fall back to the ProjectsUser approach?

One extra cookie for pointing beautiful open source Rails code, or by book indications that might help with my kind of questions.

Answer 1

I would use a specific controller. Even if now the interaction sounds simple, you can't know if in the future you'll need to add more advanced features.
I've been handling these kind of relationships in several projects, and using a controller for the join model has always paid off.

You can structure it this way, for example:

• index should expect a params[:project_id], so that you can display only the index of users for a specific project.
• create is where you add new users, that is where you create new join models.
• update is to modify a value on an existing join model, for example when you want to update the role of a user in a project.
• destroy is where you remove users from the project, that is where you delete the corresponding join models.
• You might not need a show and edit actions, if you decide to manage everything in the index view.

Also, I'd suggest to choose a different name. Rails relies heavily on naming conventions, and projects_users is the default name for the join_table you would use with a has_and_belongs_to_many association. In theory you can use it for an independent model (and a has_many through:), but it's not immediately clear and you might break something. In addiction, it will confuse the hell out of any new programmer that could join the project in the future (personal experience).

What about calling the model something like project_participation?

If you haven't built a lot of functionality yet, and don't have yet that table in production, changing it now will save you a lot of headaches in the future.

update

1) I stand by what I said earlier: your join model is a full fledged record, it holds state, can be fetched, modified (by the user) and destroyed.
A dedicated controller is the way to go. Also, this controller should handle all the operations that modify the join model, that is that alter its properties.

2) You can define User#role_for(project), just remember that it should properly handle the situation where the user is not participating to the project.

You can also make it explicit with something like:

@user.project_participations.where(project_id: @project.id).first.try(:role)
# or...
ProjectParticipation.find_by(project_id: @project.id, user_id: @user.id).try(:role)

But I'd say that encapsulating this logic in a method (on one of the two models) would be better.

3) You are already using a non standard name for your table. What I mean is that it's the default name for a different kind of association (has_and_belongs_to_many), not the one you are using (has_many through:).
Ask yourself this: is the table backing an actual model? If yes, that model represents something in the real world, and thus should have an appropriate name. If, on the other hand, the table is not backing a model (e.g. it's a join table), then you should combine the names of the tables (models) it's joining.

Answer 2

In my mind, REST doesn't always have to map directly to DB records. A conceptual resource here is the association of Projects to Users. Implementation would be different depending on your persistence layer, but a RESTful API would be standard.

Convention over Configuration in Rails is a great helper, but it isn't necessarily applicable to every case 100% of the way through the stack. There doesn't need to be a 1-to-1 mapping between controllers, models, and their respective names. At the app-level, particularly, I want my routes/controllers to represent the public view of the API, not the internal implementation details of the persistence and domain layers.

You might have a UserProjectsController which you can perform CRUD on to add/remove project associations to users, and it will do the appropriate record manipulation without being overly bound to the DB implementation. Note the naming, where the route might be /user/:id/projects, so it's clear you are manipulating not Users or Projects, but their associations.

Answer 3

I think thinking about this sort of thing (both before and after the fact) is what leads to better designs.

1. I too start with the model and think about the application structurally. The next step in my oppinion is to build the user interface to make sense based on what makes it easy and useful for the user (spending more effort on things that matter more). So if it makes sense for the user to separately edit the ProjectsUser objects then the ProjectsUsersController is the way to go. More likely editing the join model objects as part of the Project (or User depending on the structure of you app) will be a better fit for the user. In that case using a nested form and editing via the controller (and model) that's the main model referenced by the form is better. The controller really lives to serve the UI, so decisions about it should be dependent on the UI.

2. Yes, if it makes your code simpler or more readable. If you use role more than once I suspect it will.

3. I would actually name that model something like Member, or ProjectMember (or Membership). It defines a relationship between a user and a project, so its name should reflect what relationship that is. In the occasions where such a name is too unwieldly or too hard to define then falling back to something like ProjectUser is reasonable (but not ProjectsUser). But I definitely like finding a more meaningful name when possible.