如何使用ActiveRecord仅选择存储在Postgres中的json的一部分 [英] How to select only part of json, stored in Postgres, with ActiveRecord

问题描述

说我有一个模型User，它具有一个名为settings的json类型的字段.假设该字段大致如下所示:

Say I have a model User, which has a field of type json called settings. Let's assume that this field looks roughly like this:

{
  color: 'red', 
  language: 'English', 
  subitems: 
    {
      item1: true, 
      item2: 43, 
      item3: ['foo', 'bar', 'baz']
    }
}

如果我执行User.select(:settings)，我将获得每个用户的所有设置.但是我只想为用户提供语言.我都尝试过:

If I do User.select(:settings) I will get all the settings for each user. But I want to get only the languages for a user. I tried both:

User.select("settings -> 'language'")

和

User.select("settings ->> 'language'")

但这只会返回空对象:

[#<User:0x007f381fa92208 id: nil>,
...]

这有可能吗?如果是，我可以只使用json还是要切换到jsonb?

Is this at all possible? If yes - can I do it using just json or do I need to switch to jsonb?

推荐答案

尝试User.select("settings -> 'language' as user_language"). 生成关系中的每个对象都应响应user_language.

Try User.select("settings -> 'language' as user_language"). Each object in the resulting relation should respond to user_language.

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