Routing Concerns in Rails

Sometimes, you have common routes that you want to reuse inside other resources and routes. For example, imagine that your application has two resources, photos and posts.

# config/routes.rb

resources :posts
resources :photos

Next, you decide that you want to allow users to add comments under both posts and photos. That means you'll want to nest comments under both resources as follows:

# config/routes.rb

resources :posts do
  resources :comments
end

resources :photos do
  resources :comments
end

This is simple enough. But, you can imagine this can get repetitive if you have few more 'commentable' resources, i.e. resources that can be commented.

To avoid this repetition, Rails lets you to declare these common routes (concerns) to reuse inside other resources and routes. For this, you'll use the concern method as follows:

# config/routes.rb

concern :commentable do
  resources :comments
end

resources :posts, concerns: :commentable
resources :photos, concerns: :commentable

# more than one concerns are allowed
resources :messages, concerns: [:commentable, :attachable, ...]

You can also use these concerns anywhere by calling the concerns method.

# config/routes.rb

namespace :blog do
  concerns :commentable
end

The underlying idea behind routing concerns is exactly similar to the concept of concerns in Rails: to group commonly used, related code together in one place.

Concerns in Rails: Everything You Need to Know

Concerns are an important concept in Rails that can be confusing to understand for those new to Rails as well as seasoned practitioners. This post explains what concerns are, how they work, and how & when you should use them to simplify your code, with practical, real-world examples.

Write Software, WellAkshay Khot

That's a wrap. I hope you found this article helpful and you learned something new.

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