Rails模型生成了大量sql查询

Question

我有一个模型（LineItem），它是另一个（Invoice）的子模型。在LineItem中，我委托了一个引用Invoice中某个属性的方法。每当运行此方法时，它总是运行几个SQL查询。。。就好像它在重新搜索发票一样

模型"发票"
-包含属性"created_at"
-包含default_scope includes(:line_items, :payments, :sales_person)

模型"LineItem"
-包含delegate :created_at, :to => :invoice, :prefix => true
-另一种方法包括：

@tax_rate ||= (category.to_sym == :books ? invoice_created_at.federal_tax_rate : invoice_created_at.tax_rate)

正是在这种方法中生成了以下内容（使用"迷你探查器"gem）：

SELECT `invoices`.* FROM `invoices`  WHERE `invoices`.`id` = 4 LIMIT 1
SELECT `line_items`.* FROM `line_items`  WHERE `line_items`.`invoice_id` IN (4)
SELECT `items`.* FROM `items`  WHERE `items`.`id` IN (31, 15)
SELECT `categories`.* FROM `categories`  WHERE `categories`.`id` IN (6, 1) ORDER BY name
SELECT `payments`.* FROM `payments`  WHERE `payments`.`invoice_id` IN (4)
SELECT `payment_types`.* FROM `payment_types`  WHERE `payment_types`.`id` IN (1) ORDER BY name
SELECT `sales_people`.* FROM `sales_people`  WHERE `sales_people`.`id` IN (1) ORDER BY name

它对每一行项目都这样做。所有这些SELECT语句早在invoice_created_at.*tax_rate方法被调用之前就已经批量发生了。。。

SELECT `invoices`.* FROM `invoices`  WHERE (created_at between '2011-05-01 04:00:00' and '2013-02-06 04:59:59')
SELECT `line_items`.* FROM `line_items`  WHERE `line_items`.`invoice_id` IN (4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)

我该怎么做才能确保不必运行所有这些SELECT查询？

Answer 1

首先，您可以停止使用default_scope includes——在典型情况下不需要它，在您的情况下可能也不需要。

其次，更重要的是，您应该在关联上声明:inverse_of属性，以最大限度地减少重新加载内存中已经存在的对象：

class Invoice < ActiveRecord::Base
  has_many :line_items, :inverse_of => :invoice
end
class LineItem < ActiveRecord::Base
  belongs_to :invoice, :inverse_of => :line_items
end