ActiveRecord 包括.指定包含的列 [英] ActiveRecord includes. Specify included columns

问题描述

我有模型简介.个人资料 has_one 用户.用户模型具有字段电子邮件.当我打电话

I have model Profile. Profile has_one User. User model has field email. When I call

Profile.some_scope.includes(:user)

它调用

SELECT users.* FROM users WHERE users.id IN (some ids)

但是我的用户模型有很多我没有在渲染中使用的字段.是否可以只加载来自用户的电子邮件?所以，SQL 应该看起来像

But my User model has many fields that I am not using in rendering. Is it possible to load only emails from users? So, SQL should look like

SELECT users.email FROM users WHERE users.id IN (some ids)

推荐答案

Rails 无法为 include 查询传递选项.但是我们可以通过模型下的关联声明来传递这些参数.

Rails doesn't have the facility to pass the options for include query. But we can pass these params with the association declaration under the model.

对于您的场景，您需要在配置文件模型下创建与用户模型的新关联，如下所示

For your scenario, you need to create a new association with users model under the profile model, like below

belongs_to :user_only_fetch_email, :select => "users.id, users.email", :class_name => "User"

我刚刚又创建了一个关联，但它仅指向用户模型.所以你的查询将是，

I just created one more association but it points to User model only. So your query will be,

Profile.includes(:user_only_fetch_email)

或

Profile.includes(:user_only_fetch_email).find(some_profile_ids)

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