Ruby on Rails - 通过活动记录 has_many 关联减少列

发布于 2025-01-01 02:06:29 字数 1031 浏览 3 评论 0原文

我正在构建一个具有库存控制和购物车的电子商务应用程序。当付款被批准后，我想减少购物车中每种产品的数量。这意味着，我需要减少属于购物车的 line_items 的产品数量列。

我可以通过活动记录接口递减一个，如下所示（在我的购物车模型中）：

self.line_items[0].product.decrement(:qty)

也可以直接执行查询：

connection.execute("UPDATE products SET qty = qty - 1 WHERE id IN (SELECT product_id FROM line_items WHERE cart_id = #{self.cart_id})")

但这两种方法似乎都不正确。后者直接查询数据库模式，这显然不是最佳实践。第一种方法更好，但我不知道如何在所有记录上实现它。

我的模型是这样的：

class Product < ActiveRecord::Base
end

class Cart < ActiveRecord::Base  
  has_many :line_items
end

class LineItem < ActiveRecord::Base
  belongs_to :cart
  belongs_to :product
end

架构是：

create_table "carts", :force => true do |t|
  ..
end

create_table "line_items", :force => true do |t|
  ..
  t.integer  "product_id"
  t.integer  "cart_id"
end

create_table "products", :force => true do |t|
  ..
  t.integer  "qty"
end

我确信有一种优雅的方法可以做到这一点。有人可以帮我吗？

非常感谢，
轮缘

原文

I'm building an ecommerce application with inventory control and a shopping cart. When the payment has been approved, I want to decrement the quantity of each of the products in the cart. This means, I need to decrement the product quantity column which belongs to line_items which belongs to carts.

I can decrement one through the active record interface like this (in my cart model):

self.line_items[0].product.decrement(:qty)

And also by executing a query directly:

connection.execute("UPDATE products SET qty = qty - 1 WHERE id IN (SELECT product_id FROM line_items WHERE cart_id = #{self.cart_id})")

But both of these methods don't seem right. The latter queries the db schema directly which is obviously not the best practice. The first method is better but I don't know how to implement it on all the records.

My models are like so:

class Product < ActiveRecord::Base
end

class Cart < ActiveRecord::Base  
  has_many :line_items
end

class LineItem < ActiveRecord::Base
  belongs_to :cart
  belongs_to :product
end

The schema is:

create_table "carts", :force => true do |t|
  ..
end

create_table "line_items", :force => true do |t|
  ..
  t.integer  "product_id"
  t.integer  "cart_id"
end

create_table "products", :force => true do |t|
  ..
  t.integer  "qty"
end

I am sure there is an elegant way to do this. Can anyone help me please?

Many thanks,
Rim

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唔猫 2025-01-08 02:06:29

update_counters怎么样？ http://apidock.com/rails/ActiveRecord/CounterCache/update_counters

class Cart < ActiveRecord::Base  
  has_many :line_items
  has_many :products, :through => :line_items
end

Product.update_counters(cart.products, :qty => -1)
# => UPDATE "products" SET "qty" = COALESCE("qty", 0) - 1 WHERE "products"."id" IN (1, 2)

How about update_counters? http://apidock.com/rails/ActiveRecord/CounterCache/update_counters

class Cart < ActiveRecord::Base  
  has_many :line_items
  has_many :products, :through => :line_items
end

Product.update_counters(cart.products, :qty => -1)
# => UPDATE "products" SET "qty" = COALESCE("qty", 0) - 1 WHERE "products"."id" IN (1, 2)

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