Rails nested resources and routing - how to break up controllers?

All you are doing with nested resources is changing the routing URL. Only thing you would have to do is make sure you are passing the proper id (in your case post)to the tag controller. Most common error is the Can't Find *** ID.

If you don't nest a profile route into a user route it would look like this

domain.com/user/1

domain.com/profile/2

When you nest the routes it would be

domain.com/user/1/profile/2

That is all that it is doing and nothing else. You don't need additional controllers. Doing nested routing is just for looks. allowing your user to follow the association. The most important thing about nesting routes is that you make sure you make the link_to's to the right path.

When not nested: it would be

 user_path

and

 profile_path

when it is nested you would need to use

user_profile_path

rake routes is your friend to find out how the routes have changed.

Hope it helps.

I think the best solution is to split up controllers:

    resources :tags

    resources :posts do
      resources :tags, controller: 'post_tags'
    end

And then you have 3 controllers. Optionally, you can inherit PostTagsController from TagsController to do something like:

    class PostTagsController < TagsController
        def index
            @tags = Post.find(params[:post_id]).tags
            super
        end
    end

If the difference is only the retrieval of tags, you can:

    class TagsController < ApplicationController
        def tags
            Tag.all
        end

        def tag
            tags.find params[:id]
        end

        def index
            @tags = tags
            # ...
        end
        # ...
    end

    class PostTagsController < TagsController
        def tags
            Product.find(params[:product_id]).tags
        end
    end

Use that methods and simply override tags in the inheriting controllers ;)