看了 Agile Web Develoment with Rails 后，跟着写 Depot 的代码，用 scaffold 生产脚手架。y 有些地方的代码，很不理解，为什么 create 成功后就到了 show.html.erb 呢。

def create
    @product = Product.new(params[:product])

    respond_to do |format|
      if @product.save
        format.html { redirect_to @product, notice: 'Product was successfully created.' }
        format.json { render json: @product, status: :created, location: @product }
      else
        format.html { render action: "new" }
        format.json { render json: @product.errors, status: :unprocessable_entity }
      end
    end
  end

redirect_to @product，为什么就到了 show.html.erb 呢