Андрей Щетинин

match 'url' => 'controller#method', :constraints => { :only_ajax => true }

class BooksController < ApplicationController
  before_action :access_check, only:[:new]
  def new
    @book = Book.new
    form_html = render_to_string( :partial => 'books/form', :formats => [:html], :locals => { :book => @book } )
    render :json => { :form_html => form_html }
  end
  private
    def access_check
      unless request.xhr?
         redirect_to :root_path
      end
    end
end