class RecipesController < ApplicationController
    before_action :authenticate_chef!, except: [:index, :show]
    def show
        @recipe = Recipe.find(params[:id])
        @comments = @recipe.comment_threads.order('created_at desc')
        @user_who_commented = current_chef
        @new_comment = Comment.build_from(@recipe, @user_who_commented.id, "")
    end
...

class CommentsController < ApplicationController
  before_action :authenticate_chef!

  def create
    commentable = commentable_type.constantize.find(commentable_id)
    @user_who_commented = current_chef
    @comment = Comment.build_from(commentable, @user_who_commented.id, body)

    respond_to do |format|
      if @comment.save
        make_child_comment
        format.html  { redirect_to(:back, :notice => 'Comment was successfully added.') }
      else
        format.html  { render :action => "new" }
      end
    end
  end
...

class Recipe < ActiveRecord::Base
    acts_as_commentable
...

<%= render partial: "comments/template", locals: {commentable: @recipe, new_comment: @comment} %>

<% if current_user_id? %>
 заданное значение current_chef
<% else %>
  Войдите чтобы ответить
<% end %>