在Rails中防止N + 1查询 [英] Preventing N+1 queries in Rails

问题描述

我已经看到了一些示例，这些示例在调用ActiveRecord的 find 方法之一时传递：include 哈希值的例子在Rails中。但是，我还没有任何有关通过关系方法是否可行的示例。例如，假设我有以下内容：

I've seen a few examples of passing an :include hash value when calling one of ActiveRecord's find methods in Rails. However, I haven't seen any examples of whether this is possible via relationship methods. For example, let's say I have the following:

def User < ActiveRecord::Base
  has_many :user_favorites
  has_many :favorites, :through => :user_favorites
end

def Favorite < ActiveRecord::Base
  has_many :user_favorites
  has_many :users, :through => :user_favorites
end

def UserFavorite < ActiveRecord::Base
  belongs_to :user
  belongs_to :favorite
end

我看到的所有示例都显示如下代码：

All the examples I see show code like this:

User.find(:all, :include => :favorite)

但我看不到任何显示使用关系的示例。相反，我可以做这样的事情吗？

But I don't see any examples showing the use of relationships. Would it instead be possible for me to do something like this?

User.favorites(:include => :user)

推荐答案

您不能将关系用作Class方法。它是实例方法。您可以致电

You can't use relations as Class methods. It is instance methods. You can call

@user.favorites

查看此有关热切加载的截屏视频

Check out this screencast about Eager Loading

http://railscasts.com/episodes/22-eager-loading

将会

 User.find(:all, :include => :favorites)

或for Rails 3.x

or for Rails 3.x

 User.includes(:favorites)

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