Rails 3 - Restricting formats for action in resource routes

I have a resource defined in my routes.

resources :categories

And I have the following in my Category controller:

  def show
    @category = Category.find(params[:id])

    respond_to do |format|
      format.json { render :json => @category }
      format.xml  { render :xml => @category }
    end
  end

The controller action works fine for json and xml. However I do NOT want the controller to respond to html format requests. How can I only allow json and xml? This should only happen in the show action.

What is the best way to achieve this? Al开发者_开发问答so is there any good tips for DRYing up the respond_to block?

Thanks for your help.

---

I found that this seemed to work (thanks to @Pan for pointing me in the right direction):

resources :categories, :except => [:show]
resources :categories, :only => [:show], :defaults => { :format => 'json' }

The above seems to force the router into serving a format-less request, to the show action, as json by default.

---

You must wrap those routes in a scope if you want to restrict them to a specific format (e.g. html or json). Constraints unfortunately don't work as expected in this case.

This is an example of such a block...

scope :format => true, :constraints => { :format => 'json' } do
  get '/bar' => "bar#index_with_json"
end

More information can be found here: https://github.com/rails/rails/issues/5548

This answer is copied from my previous answer here..

Rails Routes - Limiting the available formats for a resource

---

You could do the following in your routes.rb file to make sure that only the show action is constrained to json or xml:

resources :categories, :except => [:show]
resources :categories, :only => [:show], :constraints => {:format => /(json|xml)/}

If this doesn't work you could try explicitly matching the action:

resources :categories, :except => [:show]
match 'categories/:id.:format' => 'categories#show', :constraints => {:format => /(json|xml)/}

---

constraints was not working for POST requests and then I tried defaults it works for all.

namespace :api, :defaults => { :format => 'json' } do
    namespace :v1 do
      resources :users do
        collection do
          get 'profile'
        end
      end
      post 'signup' => 'users#create'
      post 'login' => 'user_sessions#create'
  end
end

I was using Rails 4.2.7