CartsController#destroy 中的 NoMethodError - 使用 Rails 4 进行敏捷 Web 开发 [英] NoMethodError in CartsController#destroy - Agile Web Development with Rails 4
问题描述
我正在按照《使用 Rails 4 进行敏捷 Web 开发》这本书学习 Rails,但遇到了这个错误:
I'm learning Rails following the book Agile Web Development with Rails 4 and I got stuck with this Error:
NoMethodError in CartsController#destroy
undefined method `name' for nil:NilClass
这是 Cart 控制器的 Destroy 操作.错误信息引用了行 @cart.destroy if @cart.id == session[:cart_id]
:
This is the action Destroy of the Cart controller. The error info references to the line @cart.destroy if @cart.id == session[:cart_id]
:
# 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
这个动作是从views/carts/shown.html.erb
<%= button_to 'Empty cart', @cart, method: :delete, data: {confirm: 'Are you sure?'} %>
一切正常,但在创建将 price
列添加到表 LineItems
的迁移并修改 add_product
中的方法后 add_product
code>Carts 用于处理这个新列,destroy 操作不再起作用.
Everything was working fine, but after creating a migration that added the column price
to the table LineItems
and modifying the method add_product
from Carts
for handling this new column, the destroy action is not working anymore.
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
这是来自 line_items_controller
的操作 create
,用于将产品添加到购物车:
And this is the action create
from line_items_controller
that is used for adding products to the Cart:
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 CurrentCart
模块中的 set_cart
方法:
Before this action, the method set_cart
from the module CurrentCart
is called:
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 Cart 中 destroy
操作的测试:
When I run the controllers tests there are no failures. This is the test for the action destroy
from Cart:
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,我需要你的帮助.
I can't see what is the cause of this error and I would like your help.
编辑
这是来自服务器的输出:
This is the output from the server:
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:)
推荐答案
从 rails 控制台尝试并得到这个:
Tried from rails console and got this:
2.2.0 :001 > carro = Cart.find(25)
Cart Load (12.9ms) SELECT "carts".* FROM "carts" WHERE "carts"."id" = ? LIMIT 1 [["id", 25]]
=> #<Cart id: 25, created_at: "2015-02-17 01:10:49", updated_at: "2015-02-17 01:10:49">
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 /home/xx/.rvm/gems/ruby-2.2.0/gems/activerecord-4.0.0/lib/active_record/associations/has_many_association.rb:75: 警告:循环论证参考 - 反射
是由 activerecord
中的错误引起的,根据这个 GitHub 问题一>.
What happens is that /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
is caused for a bug in activerecord
according to this GitHub issue.
我所做的是更新 rails 版本.我使用的是 rails 4.0.0
,更新到 rails 4.1.2
后问题解决了.
What I did was update the rails version. I was using rails 4.0.0
, after updating to rails 4.1.2
the problem was solved.
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