“包含"和“包含"有什么区别?和“加入"在 ActiveRecord 查询中? [英] What's the difference between "includes" and "joins" in ActiveRecord query?

问题描述

ActiveRecord 查询中的includes"和joins"有什么区别?谁能用以下两个相关模型向我解释?

What's the difference between "includes" and "joins" in ActiveRecord query? Can anyone explain to me with the following two associated models?

class Car < ActiveRecord::Base
  belongs_to :store
end

class Store < ActiveRecord::Base
  belongs_to :owner
  has_one :car
end

推荐答案

:joins 在 sql 中将表连接在一起，:includes 急切加载关联以避免 n+1问题(执行一个查询来检索记录，然后为每个加载的关联执行一个查询).

:joins joins tables together in sql, :includes eager loads associations to avoid the n+1 problem (where one query is executed to retrieve the record and then one per association which is loaded).

我建议您阅读Rails 指南中的部分以获取更多信息.

I suggest you read their sections in Rails Guides to get more info.

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