Rails 4 - Respond only to JSON and not HTML

Question

I'm trying to build an API in rails 4, and am having an issue where rails returns a 500 error instead of a 406 when using respond_to :json and trying to access the html version.

Here's an example controller demonstrating the problem:

class PostsController < ApplicationController
  respond_to :json

  def index
    @posts = Post.all
  end
end

I also have a jbuilder view for index that works when accessing via JSON. If I try accessing the route without the JSON extension, It attempts to load the HTML template (which doesn't exist) and returns a 500 error, instead of just rendering JSON or returning a 406 error.

What could be causing this? Cheers for any help.

Possible duplicate: http://stackoverflow.com/questions/14579774/respond-to-only-json-in-rails?rq=1 — Josh, Feb 24 '14 at 03:59
I did see that, but I want to know why it doesn't work with just the `respond_to :json` setting — Tom Brunoli, Feb 24 '14 at 04:33
`respond_to :json` and `respond_with @posts` properly respond with *HTTP/1.1 406 Not Acceptable* to me in Production. In Development you get a "HTTP/1.1 500 Internal Server Error" and an `ActionController::UnknownFormat` — Leonel Galán, Dec 02 '15 at 16:11
Sorry I tried to answer but my post was deleted by a moderator since I also answered the other "possible duplicate" even though this one is more clearly Rails 4. So here you go... In Rails 4, you have to pass a lambda in the route to enforce a constraint like so: `resources :posts, constraints: lambda { |req| req.format == :json }` — Sia, Jun 02 '16 at 02:23
You can see more in the second note in the Rails guide here: http://edgeguides.rubyonrails.org/routing.html#request-based-constraints — Sia, Jun 02 '16 at 02:25
@TomBrunoli please check https://stackoverflow.com/questions/15227145/get-content-type-of-request/63579270#63579270 — Bhaveshkumar, Aug 25 '20 at 13:20

csi · Answer 1 · 2015-12-02T16:03:27.463

47

I believe there are 2 parts here:
1) json only requests in rails
2) json only responses in rails

1) Configure your application controller to ensure json requests only

# app/controller/application_controller.rb  
before_action :ensure_json_request  

def ensure_json_request  
  return if request.format == :json
  render :nothing => true, :status => 406  
end

2) Configure your Rails API routes to ensure json responses only

# config/routes.rb  
MyApp::Application.routes.draw do  
  namespace :api, constraints: { format: 'json' } do  
    namespace :v1 do  
      resources :posts  
    end  
  end  
end

edited Dec 02 '15 at 16:03

answered Jun 04 '15 at 15:10

csi

9,018
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4

Instead of `params[:format] == "json" || request.headers["Accept"] =~ /json/` you can use `request.format.symbol == :json`. – ciastek Aug 24 '15 at 10:21
1

Nice call. Updated with `request.format == :json` as `symbol` is not required per this other [request format question](http://stackoverflow.com/questions/15227145/get-content-type-of-request#answer-33768811) – csi Dec 02 '15 at 15:59
6

Rather than `render :nothing => true, :status => 406` you can use `head :not_acceptable` – Eric Terry Feb 16 '16 at 16:52

score 42 · Answer 2 · answered Jul 04 '14 at 21:41

42

To avoid loading the non-existent HTML template, set the default resource type as JSON in config/routes.rb:

resources :posts, :defaults => { :format => :json }

answered Jul 04 '14 at 21:41

5

This does not provide a constraint, which is implied by the question. The idea would be that if .json format was not specified, rails would not match on the routes and continue on down the hierarchy. – Volte Jul 13 '15 at 23:59

score 22 · Answer 3 · answered Jun 02 '16 at 22:35

22

In Rails 4, you need to pass a lambda to enforce the constraint on a route.

Unfortunately, this will NOT work because it will still try to serve up (or attempt to serve up) an html template since the format is an optional parameter:

resources :posts, constraints: { format: 'json' }

This DOES work (uses the lambda):

resources :posts, constraints: lambda { |req| req.format == :json }

See the second (final) note in this section of the Rails guide.

answered Jun 02 '16 at 22:35

Sia

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50

This doesn't seem to work with `scope`, however `defaults: { format: 'json' }` does work. – Akash Agarwal Jan 15 '18 at 18:23

score 5 · Answer 4 · answered Feb 24 '14 at 08:40

5

As you are using a before_filter, you will have a 406 Not Acceptable if a request for a format is made which is not defined.

Example:

class SomeController < ApplicationController
  respond_to :json


  def show
    @record = Record.find params[:id]

    respond_with @record
  end
end

The other way would be to add a before_filter to check for the format and react accordingly.

Example:

class ApplicationController < ActionController::Base
  before_filter :check_format


  def check_format
    render :nothing => true, :status => 406 unless params[:format] == 'json'
  end
end

But i think, you can just do it:

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

Further informations: http://guides.rubyonrails.org/layouts_and_rendering.html

answered Feb 24 '14 at 08:40

Franzé Jr.

1,194
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1

The problem I have with this is that the `respond_to :json` still lets html responses go through. I want all responses to be JSON, regardless of the requested format. – Tom Brunoli Feb 24 '14 at 21:55
Did you create your json on the view? – Franzé Jr. Oct 01 '14 at 18:40
`params[:format] == 'json'` is not enough. When request is made with `Accept: application/json` header, params[:format] is empty, but Rails still responds with JSON. – ciastek Aug 24 '15 at 10:22

score 5 · Answer 5 · answered Mar 06 '16 at 07:53

5

You can try this, as I was also facing this issue and now it is solved by using this solution.

class PostsController < ApplicationController
  respond_to :json

  def index
    @posts = Post.all
    render json: @posts
  end
end

answered Mar 06 '16 at 07:53

Shubham Abrol

613
6
10

score 4 · Answer 6 · answered Jul 17 '16 at 00:34

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

score 1 · Answer 7 · answered Sep 15 '15 at 16:09

1

You can set it by having a before filter that sets the request to JSON explicitly.

request.format = :json

answered Sep 15 '15 at 16:09

Piotr Usewicz

620
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score 0 · Answer 8 · answered Apr 01 '16 at 16:26

0

when you try a responses in json is beacuse you only need some properties i used this

@my_model=Model.select(:attributeN, :attributeN......, attributeN)
respond_to do |format|
  format.json {
    render json: @my_model
  }
end

answered Apr 01 '16 at 16:26

Ezequiel García

2,616
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12

score 0 · Answer 9 · answered Apr 01 '16 at 16:46

I would suggest you to try gem 'active_model_serializers'. Its really awesome and keeps clean.

ApplicationController:

class ApplicationController < ActionController::Base
  protect_from_forgery with: :exception, if: Proc.new { |c| c.request.format != 'application/json' }
  protect_from_forgery with: :null_session, if: Proc.new { |c| c.request.format == 'application/json' }
end

Routes:

namespace :api, defaults: { format: :json } do
    resource :posts
end

Posts Controller:

def index
   render json: Post.all
end

score 0 · Answer 10 · answered Oct 20 '20 at 18:31

0

I'm a bit late to this but regarding your comment to this answer:

I want all responses to be JSON

The easiest solution would be:

respond_to do |format|
  format.all { render :json => @posts }
end

answered Oct 20 '20 at 18:31

Lerk

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Rails 4 - Respond only to JSON and not HTML

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