查询中的虚拟属性 [英] virtual attribute in a query

问题描述

用户模型具有 all_scores 属性，我在下面创建了方法

User model has all_scores attribute and i created the method below

models/user.rb

models/user.rb

def score
  ActiveSupport::JSON.decode(self.all_scores)["local"]
end

我正在尝试使用此虚拟属性得分来过滤用户的操作.例如:我需要分数超过50的用户.问题是我不能在查询中使用虚拟属性作为常规属性.

What i'm trying to do this using this virtual attribute score to filter users. For example: I need the users whose score is over 50. The problem is i can't use virtual attribute as a regular attribute in a query.

User.where("score > 50") # i can't do this.

任何帮助将不胜感激.

推荐答案

最简单"的解决方案可能是 User.all.select {| user |user.score>50} .显然，将每个用户记录从数据库中拉出是非常低效的.

Well, the "easiest" solution would probably be User.all.select{|user| user.score > 50}. Obviously that's very inefficient, pulling every User record out of the database.

如果要查询涉及分数的信息，为什么不将 score 列添加到users表?每当更改 all_scores 时，您都可以对其进行更新.

If you want to do a query involving the score, why don't you add a score column to the users table? You could update it whenever all_scores is changed.

class User < AR::Base
  before_save :set_score, :if => :all_scores_changed?

  protected
  def set_score
    self.score = ActiveSupport::JSON.decode(self.all_scores)["local"] rescue nil
  end
end

这还将避​​免每次访问 user#score 时都不断反序列化JSON数据.

This will also avoid constantly deserializing JSON data whenever you access user#score.

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