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

Answer 1

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

request.format = :json

Answer 2

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

Answer 3

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.

Answer 4

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