Stack Overflow 10253366

# controllers/api/api_controller.rb
class Api::ApiController < ApplicationController

  respond_to :json

  before_filter :ensure_user

  rescue_from ::ApiException do |exception|
    logger.info "ApiException #{exception.inspect}"
    render :json => { :errors => { :error => exception.message} }.to_json, :status => 400
  end

  private

    def ensure_user
      unless current_user
        render :json => { :errors => { :error => 'Not authenticated'} }.to_json, :status => 401
        false
      end
    end

end

# controllers/api/v1/some_controller.rb
class Api::V1::SomeController < Api::ApiController

  def index
    # any errors here would be caught in the parent controller
  end

end