Agile Web Development Smarter Card Nil проблемы

Question

Я НОВЫЙ ПО УЧЕНИКУ Ruby on Rails. Я следую за книгой Agile Web Development с Rails 4. Я почти закончил главу 10: «Умная карта». Я должен создать модели для моделей LineItem и Cart, которые возвращают общую цену для отдельного элемента и всей карты. Когда я запускаю свой сервер, я получаю уведомление об ошибке «nil не может быть принудительно введен в BigDecimal».

Что было странно: это сработало.

Started GET "/carts/38" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 
    Processing by CartsController#show as HTML 
    Parameters: {"id"=>"38"} 
    Cart Load (0.1ms) SELECT "carts".* FROM "carts" WHERE "carts"."id" = ? LIMIT 1  [["id", 38]] 
    LineItem Load (0.1ms) SELECT "line_items".* FROM "line_items" WHERE "line_items"."cart_id" = ? [["cart_id", 38]] 
    Product Load (0.1ms) SELECT "products".* FROM "products" WHERE "products"."id" = ? LIMIT 1 [["id", 4]] 
    Rendered carts/show.html.erb within layouts/application (4.3ms) 
    Completed 200 OK in 51ms (Views: 49.2ms | ActiveRecord: 0.3ms) 


    Started GET "/assets/turbolinks.js?body=1" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started GET "/assets/application.css?body=1" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started GET "/assets/carts.js?body=1" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started GET "/assets/jquery.js?body=1" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started GET "/assets/jquery_ujs.js?body=1" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started GET "/assets/line_items.js?body=1" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started GET "/assets/store.js?body=1" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started GET "/assets/products.js?body=1" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started GET "/assets/application.js?body=1" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started GET "/assets/logo.png" for 127.0.0.1 at 2014-10-24 22:16:41 +0200 


    Started DELETE "/carts/38" for 127.0.0.1 at 2014-10-24 22:19:11 +0200 
    Processing by CartsController#destroy as HTML 
    Parameters: {"authenticity_token"=>"EhOlirn9iTrL0fXoxCLWWKQSsSPN4lNWoF0Rv2M873M=", "id"=>"38"} 
    Cart Load (0.1ms) SELECT "carts".* FROM "carts" WHERE "carts"."id" = ? LIMIT 1 [["id", 38]] 
(0.1ms) begin transaction 
    LineItem Load (0.1ms) SELECT "line_items".* FROM "line_items" WHERE "line_items"."cart_id" = ? [["cart_id", 38]] 
SQL (0.3ms) DELETE FROM "line_items" WHERE "line_items"."id" = ? [["id", 35]] 
SQL (0.1ms) DELETE FROM "carts" WHERE "carts"."id" = ? [["id", 38]] 
(0.6ms) commit transaction 
Redirected to http://0.0.0.0:3000/ 
Completed 302 Found in 4ms (ActiveRecord: 1.2ms) 

После того, как я нажал кнопку «Пустая корзина» и нажал кнопку обновления, я получил ошибку.

Started GET "/carts/36" for 127.0.0.1 at 2014-10-24 23:18:29 +0200 
ActiveRecord::SchemaMigration Load (0.4ms) SELECT "schema_migrations".* FROM  "schema_migrations" 
Processing by CartsController#show as HTML 
Parameters: {"id"=>"36"} 
Cart Load (0.2ms) SELECT "carts".* FROM "carts" WHERE "carts"."id" = ? LIMIT 1  [["id", 39]] 
    LineItem Load (0.7ms) SELECT "line_items".* FROM "line_items" WHERE "line_items"."cart_id" = ? [["cart_id", 39]] 
    Product Load (0.2ms) SELECT "products".* FROM "products" WHERE "products"."id" = ? LIMIT 1 [["id", 4]] 
    Rendered carts/show.html.erb within layouts/application (67.2ms) 
Completed 500 Internal Server Error in 96ms 

ActionView::Template::Error (nil can't be coerced into BigDecimal): 
    9:  <tr> 
    10:  <td><%= item.quantity %>&times;</td> 
    11:  <td><%= item.product.title %></td> 
    12:  <td class="item_price"><%= number_to_currency(item.total_price) %></td> 
    13: </tr> 
    14: <% end %> 
    15: 
app/models/line_item.rb:9:in `*' 
app/models/line_item.rb:9:in `total_price' 
app/views/carts/show.html.erb:12:in `block in _ app_views_carts_show_html_erb___3008945911568791515_70186161526860' 
app/views/carts/show.html.erb:8:in ` _app_views_carts_show_html_erb___3008945911568791515_70186161526860' 


Rendered /Users/eichmann/.rvm/gems/ruby-2.1.2/gems/actionpack- 4.1.4/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (1.4ms) 
Rendered /Users/eichmann/.rvm/gems/ruby-2.1.2/gems/actionpack-4.1.4/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb (0.9ms) 
Rendered /Users/eichmann/.rvm/gems/ruby-2.1.2/gems/actionpack-4.1.4/lib/action_dispatch/middleware/templates/rescues/template_error.html.erb within rescues/layout (12.8ms) 

Модель Корзина

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



    def add_product(product_id) 
    current_item = line_items.find_by(product_id: product_id) 
    if current_item 
    current_item.quantity = current_item.quantity.to_i + 1 
    else 
    current_item = line_items.build(product_id: product_id) 
    end 
    current_item 
    end 

def total_price 
    line_items.to_a.sum { |item| item.total_price } 
end 
end 

Модель из LineItem

class LineItem < ActiveRecord::Base 
    belongs_to :product 
    belongs_to :cart 
    validates :product_id, presence: true 
    validates :cart_id, presence: true 


    def total_price 
    product.price * quantity 
    end 
    end 

Просмотр Телеги Показывать

<% if notice %> 
 
<%= notice %> 
 
<p id="notice"><%= notice %></p> 
 
<% end %> 
 

 
<h2>Your Cart </h2> 
 
<table> 
 
    <% @cart.line_items.each do |item| %> 
 
    <tr> 
 
     <td><%= item.quantity %>&times;</td> 
 
     <td><%= item.product.title %></td> 
 
     <td class="item_price"><%= number_to_currency(item.total_price) %></td> 
 
    </tr> 
 
<% end %> 
 

 
<tr class="total_line"> 
 
    <td colspan="2">Total</td> 
 
    <td class="total_cell"><%= number_to_currency(@cart.total_price)%></td> 
 
</tr> 
 
</table> 
 

 

 
<%= link_to 'Empty cart', @cart, method: :delete, data: { confirm: 'Are you sure?' } %>

def destroy @ line_item.destroy reply_to do | формат | format.html {redirect_to line_items_url, note: 'Позиция успешно уничтожена.' } format.json {голова: no_content} конец конец

private 
    # Use callbacks to share common setup or constraints between actions. 
    def set_line_item 
    @line_item = LineItem.find(params[:product_id]) 
    end 
end 

# Never trust parameters from the scary internet, only allow the white list through. 
def line_item_params 
    params.require(:line_item).permit(:product_id) 
end 

Controller Card

def create 
 
    @cart = Cart.new(cart_params) 
 

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

Корзина Контроллер уничтожить

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 

Мой дб

class AddQuantityToLineItems < ActiveRecord::Migration 
    def change 
    add_column :line_items, :quantity, :integer, default: 0 
    end 
end 

Answer 1

одного количество этого из позиций является nil. В total_price вы пытаетесь умножить price на nil, что приводит к ошибке.

Я бы рекомендовал добавить значение по умолчанию для столбца в базе данных - количество Line_Item должен по умолчанию 0.