ruby​​エラーを理解できません

Question

OK、私は "Agile Web Development with Rails"を読んでデポアプリケーションで作業しています。この本を持っている人は、第9.3章「反復D3：ボタンを追加する」です。

我々は、我々はそれがApplicationControllerには、私たちのカートへのアクセス権を持つ拡張作成任意のコントローラを、それを作る私たちの「ショッピングカート」

class ApplicationController < ActionController::Base 

    protect_from_forgery 

    private 
    def current_cart 
     Cart.find(session[:cart_id]) 
    rescue ActiveRecord::RecordNotFound 
     cart = Cart.create 
     session[:cart_id] = cart.id 
     cart 
    end 
end 

を保持するために、セッションを作成し、このセクションに先立ち。

このセクションでは、ApplicationControlerを拡張するLineItemsControllerクラスの「作成」機能を編集します。

オリジナルの作成方法は、この

def create 
    @line_item = LineItem.new(params[:line_item]) 

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

のように見える本は、このような場合には変更すると言います。

def create 
    @cart = current_cart 

    product = Product.find(params[:product_id]) 

    @line_item = @cart.line_items.build(product: product) 

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

コードを3回チェックしました。私は本からそれを複製しました。ルビーの専門家ではない私は何が欠けているのか分からない。それが私に与えるエラーはこれです。

ArgumentError in LineItemsController#create 

wrong number of arguments (0 for 1) 
Rails.root: /Users/jandrews/Projects/pragprog_ruby/depot 

Application Trace | Framework Trace | Full Trace 
activerecord (3.1.3) lib/active_record/relation.rb:318:in `destroy' 
activerecord (3.1.3) lib/active_record/base.rb:442:in `destroy' 
app/models/cart.rb:2:in `<class:Cart>' 
app/models/cart.rb:1:in `<top (required)>' 
activesupport (3.1.3) lib/active_support/dependencies.rb:456:in `load' 
activesupport (3.1.3) lib/active_support/dependencies.rb:456:in `block in load_file' 
activesupport (3.1.3) lib/active_support/dependencies.rb:640:in `new_constants_in' 
activesupport (3.1.3) lib/active_support/dependencies.rb:455:in `load_file' 
activesupport (3.1.3) lib/active_support/dependencies.rb:342:in `require_or_load' 
activesupport (3.1.3) lib/active_support/dependencies.rb:489:in `load_missing_constant' 
activesupport (3.1.3) lib/active_support/dependencies.rb:181:in `block in const_missing' 
activesupport (3.1.3) lib/active_support/dependencies.rb:179:in `each' 
activesupport (3.1.3) lib/active_support/dependencies.rb:179:in `const_missing' 
activesupport (3.1.3) lib/active_support/dependencies.rb:501:in `load_missing_constant' 
activesupport (3.1.3) lib/active_support/dependencies.rb:181:in `block in const_missing' 
activesupport (3.1.3) lib/active_support/dependencies.rb:179:in `each' 
activesupport (3.1.3) lib/active_support/dependencies.rb:179:in `const_missing' 
app/controllers/application_controller.rb:7:in `current_cart' 
app/controllers/line_items_controller.rb:43:in `create' 
actionpack (3.1.3) lib/action_controller/metal/implicit_render.rb:4:in `send_action' 
actionpack (3.1.3) lib/abstract_controller/base.rb:167:in `process_action' 
actionpack (3.1.3) lib/action_controller/metal/rendering.rb:10:in `process_action' 
actionpack (3.1.3) lib/abstract_controller/callbacks.rb:18:in `block in process_action' 
activesupport (3.1.3) lib/active_support/callbacks.rb:416:in `_run__1422100127945824718__process_action__3684163507935076470__callbacks' 
activesupport (3.1.3) lib/active_support/callbacks.rb:386:in `_run_process_action_callbacks' 
activesupport (3.1.3) lib/active_support/callbacks.rb:81:in `run_callbacks' 
actionpack (3.1.3) lib/abstract_controller/callbacks.rb:17:in `process_action' 
actionpack (3.1.3) lib/action_controller/metal/rescue.rb:17:in `process_action' 
actionpack (3.1.3) lib/action_controller/metal/instrumentation.rb:30:in `block in process_action' 
activesupport (3.1.3) lib/active_support/notifications.rb:53:in `block in instrument' 
activesupport (3.1.3) lib/active_support/notifications/instrumenter.rb:21:in `instrument' 
activesupport (3.1.3) lib/active_support/notifications.rb:53:in `instrument' 
actionpack (3.1.3) lib/action_controller/metal/instrumentation.rb:29:in `process_action' 
actionpack (3.1.3) lib/action_controller/metal/params_wrapper.rb:201:in `process_action' 
activerecord (3.1.3) lib/active_record/railties/controller_runtime.rb:18:in `process_action' 
actionpack (3.1.3) lib/abstract_controller/base.rb:121:in `process' 
actionpack (3.1.3) lib/abstract_controller/rendering.rb:45:in `process' 
actionpack (3.1.3) lib/action_controller/metal.rb:193:in `dispatch' 
actionpack (3.1.3) lib/action_controller/metal/rack_delegation.rb:14:in `dispatch' 
actionpack (3.1.3) lib/action_controller/metal.rb:236:in `block in action' 
actionpack (3.1.3) lib/action_dispatch/routing/route_set.rb:65:in `call' 
actionpack (3.1.3) lib/action_dispatch/routing/route_set.rb:65:in `dispatch' 
actionpack (3.1.3) lib/action_dispatch/routing/route_set.rb:29:in `call' 
rack-mount (0.8.3) lib/rack/mount/route_set.rb:152:in `block in call' 
rack-mount (0.8.3) lib/rack/mount/code_generation.rb:96:in `block in recognize' 
rack-mount (0.8.3) lib/rack/mount/code_generation.rb:75:in `optimized_each' 
rack-mount (0.8.3) lib/rack/mount/code_generation.rb:95:in `recognize' 
rack-mount (0.8.3) lib/rack/mount/route_set.rb:141:in `call' 
actionpack (3.1.3) lib/action_dispatch/routing/route_set.rb:532:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/best_standards_support.rb:17:in `call' 
rack (1.3.6) lib/rack/etag.rb:23:in `call' 
rack (1.3.6) lib/rack/conditionalget.rb:35:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/head.rb:14:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/params_parser.rb:21:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/flash.rb:247:in `call' 
rack (1.3.6) lib/rack/session/abstract/id.rb:195:in `context' 
rack (1.3.6) lib/rack/session/abstract/id.rb:190:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/cookies.rb:331:in `call' 
activerecord (3.1.3) lib/active_record/query_cache.rb:64:in `call' 
activerecord (3.1.3) lib/active_record/connection_adapters/abstract/connection_pool.rb:477:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call' 
activesupport (3.1.3) lib/active_support/callbacks.rb:392:in `_run_call_callbacks' 
activesupport (3.1.3) lib/active_support/callbacks.rb:81:in `run_callbacks' 
actionpack (3.1.3) lib/action_dispatch/middleware/callbacks.rb:28:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/reloader.rb:68:in `call' 
rack (1.3.6) lib/rack/sendfile.rb:101:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/remote_ip.rb:48:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/show_exceptions.rb:47:in `call' 
railties (3.1.3) lib/rails/rack/logger.rb:13:in `call' 
rack (1.3.6) lib/rack/methodoverride.rb:24:in `call' 
rack (1.3.6) lib/rack/runtime.rb:17:in `call' 
activesupport (3.1.3) lib/active_support/cache/strategy/local_cache.rb:72:in `call' 
rack (1.3.6) lib/rack/lock.rb:15:in `call' 
actionpack (3.1.3) lib/action_dispatch/middleware/static.rb:53:in `call' 
railties (3.1.3) lib/rails/engine.rb:456:in `call' 
rack (1.3.6) lib/rack/content_length.rb:14:in `call' 
rack (1.3.6) lib/rack/handler/webrick.rb:59:in `service' 
/Users/jandrews/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/webrick/httpserver.rb:138:in `service' 
/Users/jandrews/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/webrick/httpserver.rb:94:in `run' 
/Users/jandrews/.rvm/rubies/ruby-1.9.3-p0/lib/ruby/1.9.1/webrick/server.rb:191:in `block in start_thread' 
Request 

Parameters: 

{"authenticity_token"=>"tx+PRUMMQpyZ48Yw9ZLoWZ60HOo1992tpQXbKFkF4YM=", 
"product_id"=>"5"} 
Show session dump 

Show env dump 

Response 

Headers: 

None 

実際にブラウザ

<form action="/line_items?product_id=5" class="button_to" method="post"> 
    <div> 
    <input type="submit" value="Add to Cart"> 
    <input name="authenticity_token" type="hidden" 
     value="tx+PRUMMQpyZ48Yw9ZLoWZ60HOo1992tpQXbKFkF4YM="> 
    </div> 
</form> 

申し訳ありませんが、このような提出ルックスは、私はそれがラインとラインに失敗し、元から一つずつを追加すると言及するのを忘れてしまったんコード。ルビーの知識がまだ限られているので、私がデバッグできた限りです。

@cart = current_cart 

カートモデルファイル。

class Cart < ActiveRecord::Base 
    has_many :line_items, dependent: destroy 
end 

Answer 1

代わりの

has_many :line_items, dependent: destroy 

はあなた `アプリ/モデル/ cart.rb`ファイルの最初の2行は何ですか

has_many :line_items, dependent: :destroy # the colon!!