inverse_of 有什么作用?它生成什么 SQL? [英] What does inverse_of do? What SQL does it generate?

问题描述

我正在尝试了解 inverse_of，但我不明白.

I'm trying to get my head around inverse_of and I do not get it.

生成的sql是什么样的，如果有的话?

What does the generated sql look like, if any?

如果与 :has_many、:belongs_to 和 :has_many_and_belongs_to 一起使用，inverse_of 选项是否表现出相同的行为>?

Does the inverse_of option exhibit the same behavior if used with :has_many, :belongs_to, and :has_many_and_belongs_to?

抱歉，这是一个如此基本的问题.

Sorry if this is such a basic question.

我看到了这个例子:

class Player < ActiveRecord::Base
  has_many :cards, :inverse_of => :player
end

class Card < ActiveRecord::Base
  belongs_to :player, :inverse_of => :cards
end

推荐答案

来自文档，看起来 :inverse_of 选项是一种避免 SQL 查询的方法，而不是生成它们.提示 ActiveRecord 使用已加载的数据，而不是通过关系再次获取它.

From the documentation, it seems like the :inverse_of option is a method for avoiding SQL queries, not generating them. It's a hint to ActiveRecord to use already loaded data instead of fetching it again through a relationship.

他们的例子:

class Dungeon < ActiveRecord::Base
  has_many :traps, :inverse_of => :dungeon
  has_one :evil_wizard, :inverse_of => :dungeon
end

class Trap < ActiveRecord::Base
  belongs_to :dungeon, :inverse_of => :traps
end

class EvilWizard < ActiveRecord::Base
  belongs_to :dungeon, :inverse_of => :evil_wizard
end

在这种情况下，调用 dungeon.traps.first.dungeon 应该返回原始的 dungeon 对象，而不是像默认情况那样加载一个新对象.

In this case, calling dungeon.traps.first.dungeon should return the original dungeon object instead of loading a new one as would be the case by default.

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