CartsController中的NoMethodError＃destroy – 使用Rails进行敏捷Web开发4
我正在学习使用Rails 4的敏捷Web开发书之后的Rails，我遇到了这个错误：
NoMethodError in CartsController#destroy undefined method `name' for nil:NilClass 这是Cart控制器的动作Destroy。 @cart.destroy if @cart.id == session[:cart_id] ，错误信息引用@cart.destroy if @cart.id == session[:cart_id]行：
# DELETE /carts/1 # DELETE /carts/1.json def destroy @cart.destroy if @cart.id == session[:cart_id] session[:cart_id] = nil respond_to do |format| format.html { redirect_to store_url, notice: 'Your cart is currently empty'} format.json { head :no_content } end end
此操作是从views/carts/shown.html.erb的“Empty car”按钮views/carts/shown.html.erb
一切都运行正常，但在创建了一个将列price添加到表LineItems并从Carts修改方法add_product以处理这个新列的迁移后，destroy动作不再起作用了。
这是models/cart.rb
class Cart < ActiveRecord::Base has_many :line_items, dependent: :destroy def add_product(product_id, product_price) current_item = line_items.find_by(product_id: product_id) if current_item current_item.quantity += 1 else current_item = line_items.build(product_id: product_id, price: product_price) end current_item end def total_price line_items.to_a.sum { |item| item.total_price } end end
这是models/line_item.rb ：
class LineItem < ActiveRecord::Base belongs_to :product belongs_to :cart def total_price price * quantity end end
这是从line_items_controller create的动作，用于将产品添加到购物车：
before_action :set_cart, only: [:create] ... # POST /line_items # POST /line_items.json def create session[:counter] = 0 product = Product.find(params[:product_id]) @line_item = @cart.add_product(product.id, product.price) respond_to do |format| if @line_item.save format.html { redirect_to @line_item.cart } format.json { render action: 'show', status: :created, location: @line_item } else format.html { render action: 'new' } format.json { render json: @line_item.errors, status: :unprocessable_entity } end end end
在此操作之前，将调用模块CurrentCart的方法set_cart ：
def set_cart @cart = Cart.find(session[:cart_id]) rescue ActiveRecord::RecordNotFound @cart = Cart.create session[:cart_id] = @cart.id end
当我运行控制器测试时，没有失败。 这是对购物车动作destroy的测试：
test "should destroy cart" do assert_difference('Cart.count', -1) do session[:cart_id] = @cart.id delete :destroy, id: @cart end assert_redirected_to store_path end
我看不出这个错误的原因是什么，我希望得到你的帮助。
编辑
这是服务器的输出：
Started DELETE "/carts/15" for 127.0.0.1 at 2015-02-16 12:23:43 -0500 Processing by CartsController#destroy as HTML Parameters: {"authenticity_token"=>"hLsBQ0fR5b9M2lfxMc5McU1+dqtnZ2OKABRZV79vdHo=", "id"=>"15"} Cart Load (0.2ms) SELECT "carts".* FROM "carts" WHERE "carts"."id" = ? LIMIT 1 [["id", "15"]] (0.2ms) begin transaction LineItem Load (0.9ms) SELECT "line_items".* FROM "line_items" WHERE "line_items"."cart_id" = ? [["cart_id", 15]] SQL (0.5ms) DELETE FROM "line_items" WHERE "line_items"."id" = ? [["id", 91]] (0.2ms) rollback transaction Completed 500 Internal Server Error in 73ms NoMethodError (undefined method `name' for nil:NilClass): app/controllers/carts_controller.rb:58:in `destroy'
谢谢 ：）
尝试从rails控制台得到这个：
2.2.0 :001 > carro = Cart.find(25) Cart Load (12.9ms) SELECT "carts".* FROM "carts" WHERE "carts"."id" = ? LIMIT 1 [["id", 25]] => # 2.2.0 :002 > carro.destroy (0.2ms) begin transaction /home/xx/.rvm/gems/ruby-2.2.0/gems/activerecord-4.0.0/lib/active_record/associations/has_many_association.rb:75: warning: circular argument reference - reflection /home/xx/.rvm/gems/ruby-2.2.0/gems/activerecord-4.0.0/lib/active_record/associations/has_many_association.rb:79: warning: circular argument reference - reflection /home/xx/.rvm/gems/ruby-2.2.0/gems/activerecord-4.0.0/lib/active_record/associations/has_many_association.rb:83: warning: circular argument reference - reflection /home/xx/.rvm/gems/ruby-2.2.0/gems/activerecord-4.0.0/lib/active_record/associations/has_many_association.rb:102: warning: circular argument reference - reflection LineItem Load (0.2ms) SELECT "line_items".* FROM "line_items" WHERE "line_items"."cart_id" = ? [["cart_id", 25]] SQL (0.3ms) DELETE FROM "line_items" WHERE "line_items"."id" = ? [["id", 116]] SQL (0.1ms) DELETE FROM "line_items" WHERE "line_items"."id" = ? [["id", 117]] SQL (0.1ms) DELETE FROM "line_items" WHERE "line_items"."id" = ? [["id", 118]] (0.2ms) rollback transaction NoMethodError: undefined method `name' for nil:NilClass from /home/xx/.rvm/gems/ruby-2.2.0/gems/activerecord-4.0.0/lib/active_record/associations/has_many_association.rb:80:in `cached_counter_attribute_name'
会发生什么是/home/xx/.rvm/gems/ruby-2.2.0/gems/activerecord-4.0.0/lib/active_record/associations/has_many_association.rb:75: warning: circular argument reference - reflection引起/home/xx/.rvm/gems/ruby-2.2.0/gems/activerecord-4.0.0/lib/active_record/associations/has_many_association.rb:75: warning: circular argument reference - reflection根据此GitHub问题 ， activerecord的错误。
我做的是更新rails版本。 我正在使用rails 4.0.0 ，在更新到rails 4.1.2 ，问题解决了。