How to break Rails application and return 404 as JSON

Question

Rails application working as API service. I use mongoid

In a controller i write now:

class UsersController < ApplicationController
  def show
    @user = User.find params[:user_id]
    unless @user
      render json: { error: I18n.t('user.messages.not_found') }, status: :not_found
      return
    end
    # ... some actions with @user object 
  end
end

I need make code cleaner and move this code in module. I assume that the code in controller may look like this:

class UsersController < ApplicationController
  def show
    @user = User.find params[:user_id]
    not_found? @user

    # ... some actions with @user object
  end
end

or like this

class UsersController < ApplicationController
  def show
    @user = found? User, params[:user_id]

    # ... some actions with @user object
  end
end

One of example how it can work is Pundit gem (https://github.com/elabs/pundit). In my controller i write:

...
def index
  authorize User, :index?
  @users = User.all
end
...

if user hasn't access to this page then Pundit raise exception and return to client error message with 401 http code.

What is better way to refactor my code to make controllers cleaner?

Answer 1

My solution:

lib/myapp/exceptions.rb

module MyApp
  module Exceptions
    class Error < StandardError; end
    class ModelNotFound < Error

      def initialize(model)
        # api_error - helper for create standart JSON-response
        @json = api_error("#{ model.model_name.plural }.#{ model.model_name.singular }_not_found")
        message = @json
        super(message)
      end

      def json
        @json
      end
    end

    def self.included(base)
      base.rescue_from MyApp::Exceptions::ModelNotFound do |e|
        render json: e.json, status: :not_found
      end
    end
  end
end

app/controllers/application_controller.rb

class ApplicationController < ActionController::Base

  ...
  include MyApp::Exceptions

  def found?(model, id)
    @model = model.find id
    return @model if @model
    raise MyApp::Exceptions::ModelNotFound.new model
  end

Sample of using:

app/controllers/users_controller.rb

class UsersController < ApplicationController
  def show
    @user = found? User, params[:user_id]

    # ... some actions with @user object
  end
end

when i execute GET request /users/77777 application returns:

{
    'code': 'users_user_not_found',
    'error': 'User not found'
}