按最近回答的问题排序并过滤特定用户未回答的问题

Question

我在编写 returns 我想要的结果的 Active Record 查询时遇到问题。我有以下设置：

删节User型号：

class User < ActiveRecord::Base
  has_many :answers
end

删节Answer型号：

class Answer < ActiveRecord::Base
  belongs_to :question
  belongs_to :user
end

删节Question型号：

class Question < ActiveRecord::Base
  has_many :answers

  def self.unanswered_by(user)
    where(
      'id NOT IN (SELECT question_id FROM answers WHERE user_id = ?)',
      user.id
    )
  end

  def self.recently_answered
    includes(:answers).order('answers.updated_at DESC')
  end
end

我试图得到一个 ActiveRecord::Relation 返回，它按最近回答的问题排序问题，然后过滤该结果，使其仅包含 current_user 尚未回答的问题.

理想情况下，我想写

Question.recently_answered.unanswered_by current_user

但这似乎不起作用，我正在努力理解为什么我对 SQL.

的理解有限

这是我在 Rails 控制台中运行得到的结果：

me = User.find(8)
Question.recently_answered.unanswered_by me
=>   SQL (0.5ms)  SELECT `questions`.`id` AS t0_r0,
     `questions`.`question_text` AS t0_r1,
     `questions`.`example_answer` AS t0_r2,
     `questions`.`created_at` AS t0_r3,
     `questions`.`updated_at` AS t0_r4,
     `answers`.`id` AS t1_r0,
     `answers`.`question_id` AS t1_r1,
     `answers`.`user_id` AS t1_r2,
     `answers`.`answer_text` AS t1_r3,
     `answers`.`created_at` AS t1_r4,
     `answers`.`updated_at` AS t1_r5
     FROM `questions` LEFT OUTER JOIN `answers`
     ON `answers`.`question_id` = `questions`.`id`
     WHERE (id NOT IN (SELECT question_id FROM answers WHERE user_id = 8))
     ORDER BY answers.updated_at DESC
     #<ActiveRecord::Relation:0x3fd42e362a80>

运行 Question.recently_answered.unanswered_by(me).to_sql 给我这个：

=> "SELECT `questions`.*
   FROM `questions`
   WHERE (id NOT IN (SELECT question_id
          FROM answers WHERE user_id = 8))
   ORDER BY answers.updated_at DESC"

我现在正在解决这个问题

Question
  .recently_answered
  .reject { |q| q.answers.map(&:user_id).include? current_user.id }

但是这个 returns Array 个 Question 个对象而不是我更喜欢的 ActiveRecord::Relation 个对象。

有人可以帮助我理解为什么我不能按照所写的那样链接 recently_answered 和 unanswered_by 以及我如何重写它以获得我想要的结果？谢谢。

Answer 1

您应该在 unanswered_by 方法的 SQL 查询中添加 table 的名称：

  def self.unanswered_by(user)
    where('questions.id NOT IN (SELECT question_id FROM answers WHERE user_id = ?)', user.id)
          #^^^^^^^^^ table's name added here
  end

因为如果您将此与 joins/includes 结合使用，您的数据库适配器将不知道您 table 来自哪个 ID（错误消息如column id is ambiguous).

此外，对于这两种方法，您可能应该使用 scope。

按最近回答的问题排序并过滤特定用户未回答的问题

Ordering questions by most recently answered and filtering those unanswered by a particular user

mysql

activerecord

ruby-on-rails

ruby-on-rails-3.2