Ruby On Rails的第一个应用（六）--创建购物车
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2022-03-02 23:53:44
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IV 任务D：创建购物车
任务列表：
·会话和会话管理
·添加模型间的关系
·创建一个按钮，可添加产品到购物车中
一、迭代D1：寻找购物车
应用程序需要跟踪所有由买家添加到购物车中的商品。所以需要把购物车放到数据库中，并在会话中存储该购物车的唯一标识符cart.id。每当请求出现时，可以从会话中找到该购物车的标识，并用该标识在数据库中查找购物车。
1.创建一个购物车：
Administrator@JARRY /e/works/ruby/depot (master)
$ rails generate scaffold cart
SECURITY WARNING: No secret option provided to Rack::Session::Cookie.
This poses a security threat. It is strongly recommended that you
provide a secret to prevent exploits that may be possible from crafted
cookies. This will not be supported in future versions of Rack, and
future versions will even invalidate your existing user cookies.
Called from: d:/dev/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/actionpack-3.2.1/lib/action_dispatch/middleware/
session/abstract_store.rb:28:in `initialize'.
invoke active_record
create db/migrate/20130319021136_create_carts.rb
create app/models/cart.rb
invoke test_unit
create test/unit/cart_test.rb
create test/fixtures/carts.yml
route resources :carts
invoke scaffold_controller
create app/controllers/carts_controller.rb
invoke erb
create app/views/carts
create app/views/carts/index.html.erb
create app/views/carts/edit.html.erb
create app/views/carts/show.html.erb
create app/views/carts/new.html.erb
create app/views/carts/_form.html.erb
invoke test_unit
create test/functional/carts_controller_test.rb
invoke helper
create app/helpers/carts_helper.rb
invoke test_unit
create test/unit/helpers/carts_helper_test.rb
invoke assets
invoke coffee
create app/assets/javascripts/carts.js.coffee
invoke scss
create app/assets/stylesheets/carts.css.scss
invoke scss
identical app/assets/stylesheets/scaffolds.css.scss
2.
Administrator@JARRY /e/works/ruby/depot (master) $ rake db:migrate == CreateCarts: migrating ==================================================== -- create_table(:carts) -> 0.0781s == CreateCarts: migrated (0.0781s) ===========================================
3.
rails会话看上去像控制器的一个散列，所以将这个购物车id放在会话中，其可以使用符号:card_id建立索引。
/app/controllers/application_controller.rb
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
二、迭代D2：将产品放到购 物车中
购物车中包含了一些选购的货品。创建rails模型并应用迁移来创建相应的数据库表
1.
Administrator@JARRY /e/works/ruby/depot (master)
$ rails generate scaffold line_item product_id:integer cart_id:integer
SECURITY WARNING: No secret option provided to Rack::Session::Cookie.
This poses a security threat. It is strongly recommended that you
provide a secret to prevent exploits that may be possible from crafted
cookies. This will not be supported in future versions of Rack, and
future versions will even invalidate your existing user cookies.
Called from: d:/dev/RailsInstaller/Ruby1.9.3/lib/ruby/gems/1.9.1/gems/actionpack-3.2.1/lib/action_dispatch/middle
ware/session/abstract_store.rb:28:in `initialize'.
invoke active_record
create db/migrate/20130319022813_create_line_items.rb
create app/models/line_item.rb
invoke test_unit
create test/unit/line_item_test.rb
create test/fixtures/line_items.yml
route resources :line_items
invoke scaffold_controller
create app/controllers/line_items_controller.rb
invoke erb
create app/views/line_items
create app/views/line_items/index.html.erb
create app/views/line_items/edit.html.erb
create app/views/line_items/show.html.erb
create app/views/line_items/new.html.erb
create app/views/line_items/_form.html.erb
invoke test_unit
create test/functional/line_items_controller_test.rb
invoke helper
create app/helpers/line_items_helper.rb
invoke test_unit
create test/unit/helpers/line_items_helper_test.rb
invoke assets
invoke coffee
create app/assets/javascripts/line_items.js.coffee
invoke scss
create app/assets/stylesheets/line_items.css.scss
invoke scss
identical app/assets/stylesheets/scaffolds.css.scss
2.
Administrator@JARRY /e/works/ruby/depot (master) $ rake db:migrate == CreateLineItems: migrating ================================================ -- create_table(:line_items) -> 0.0781s == CreateLineItems: migrated (0.0781s) =======================================
3.表建完了，现在在数据库中有地方来存放在线商品、购物车和产品之间的关系了。然而，rails应用程序并不是把这些关系放在数据库中。我们需要在模型文件中添加一些声明来说明它们之间的关系。
在/app/models下修改cart.rb添加has_many的调用：
class Cart < ActiveRecord::Base has_many :line_items, dependent: :destroy end
4.从相反的方向来定义连接，人在线商品到carts和products表。为了实现这个，要在文件line_item.rb中使用两次belongs_to声明：
/app/models/line_item.rb
class LineItem < ActiveRecord::Base belongs_to :product belongs_to :cart end
belongs_to声明放在哪里？简单地说，如果一个数据库表有外键，那么在相应的模型中每个外键都要有个belongs_to声明
5.出于完整性的考虑，应该在模型Product中也添加一个has_many指令。毕竟，如果我们有许多个购物车的话，每个产品也可以有多个在线商品引用它。这次我们用验证代码来避免删除那些正在被在线商品引用的产品。
/app/models/product.rb
class Product < ActiveRecord::Base
default_scope order: 'title'
has_many :line_items
before_destroy :ensure_not_referenced_by_any_line_item
# ... 之前的验证代码
private
#ensure that there are no line items referencing this product
def ensure_not_refrenced_by_any_line_item
if line_items.empty?
return true
else
errors.add(:base, 'Line Items present')
return false
end
end
end
三、迭代D3：添加一个按钮
模型间的关系处理完毕，该给每个产品添加一个Add to Cart按钮了。
我们不必创建新的控制器，甚至不必创建一个新的行为。脚手架生成器提供了：index、show、new、edit、create、update和destroy。我们正好可用的行为create。（行为new可能听上去也差不多，但是这个行为通常是要获得一个表单，可在其中输入某些信息，然后再由行为create继续下去。）
1.添加链接前我们使用了link_to，但链接默认使用http get方法。这里我们想用post，所以这次我们需要添加一个按钮，要用button_to方法。
可以通过指定url来将按钮和在线商品联系起来，但是rails可简单地将_path追加到控制器的名称后，用rails来处理，这里可以用line_items_path。
现在问题是哪个产品要添加到购物车中呢？这就需要把对应的产品id也传给这个方法。
/app/views/store/index.html.erb
<% if notice %> <p id="notice"><%= notice %></p> <% end %> <h1>Your Pragmatic Catalog</h1> <% @products.each do |product| %> <div class="entry"> <%= image_tag(product.image_url) %> <h3><%= product.title %></h3> <%= sanitize(product.description) %> <div class="price_line"> <span class="price"><%= number_to_currency(product.price, unit: "￥") %></span> <%= button_to 'Add to Cart', line_items_path(product_id: product) %> </div> </div> <% end %>
2.
/app/assets/stylesheets/store.css.scss
// Place all the styles related to the Store controller here.
// They will automatically be included in application.css.
// You can use Sass (SCSS) here: http://sass-lang.com/
/* START_HIGHLIGHT */
.store {
h1 {
margin: 0;
padding-bottom: 0.5em;
font: 150% sans-serif;
color: #226;
border-bottom: 3px dotted #77d;
}
/* An entry in the store catalog */
.entry {
overflow: auto;
margin-top: 1em;
border-bottom: 1px dotted #77d;
min-height: 100px;
img {
width: 80px;
margin-right: 5px;
margin-bottom: 5px;
position: absolute;
}
h3 {
font-size: 120%;
font-family: sans-serif;
margin-left: 100px;
margin-top: 0;
margin-bottom: 2px;
color: #227;
}
//#START:inline
p, div.price_line {
margin-left: 100px;
margin-top: 0.5em;
margin-bottom: 0.8em;
/* START_HIGHLIGHT */
form, div {
display: inline;
}
/* END_HIGHLIGHT */
}
//#END:inline
.price {
color: #44a;
font-weight: bold;
margin-right: 3em;
}
}
}
/* END_HIGHLIGHT */
3.添加按钮后效果
4.现在我们来修改LineItemsContorller以找到购物车中的内容。我们需要做的只是在/app/controllers/line_items_controller.rb的create方法中修改几行代码：
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
5.每当修改控制器功能时，我们知道需要更新相应的功能测试。在调用create方法时需要传递产品id给该方法，并将重定向的网址修改为我们想要的。通过修改/test/functional/line_items_controller_test.rb实现：
test "should create line_item" do
assert_difference('LineItem.count') do
post :create, product_id: products(:ruby).id
end
assert_redirected_to cart_path(assigns(:line_item).cart)
end
6.rake test:functionals
7.显示购物车，创建简单的模板，/app/views/carts/show.html.erb：
<h2>Your Pragmatic Cart<h2> <ul> <% @cart.line_items.each do |item| %> <li><%= item.product.title %></li> <% end %> </ul>
8.点击add to cart添加到购物车后
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