ruby-on-rails - 内部联接上的 Rails ActiveRecord 子查询

Question

我正在努力使用 Rails 的 ActiveRecord 查询接口(interface)来复制具有内部联接子查询的查询。我将如何复制以下内容:

SELECT ass.name, COUNT(DISTINCT a.question_id) AS 
  answered_questions, tq.total_questions
  FROM assessments AS ass
  INNER JOIN  (SELECT ass.id, COUNT(q.id) AS total_questions FROM                         
    questions AS q INNER JOIN assessments AS ass ON ass.id=q.assessment_id 
    GROUP BY 
    ass.id) as tq ON tq.id=ass.id
  INNER JOIN questions AS q ON q.assessment_id=ass.id
  INNER JOIN answers AS a ON a.assessment_id=ass.id AND a.question_id=q.id
  INNER JOIN org_assesments AS oa ON ass.id=oa.assessment_id
  INNER JOIN users AS u ON oa.org_id=u.org_id AND       
    a.user_id=u.id
  WHERE  u.id=1
  GROUP BY ass.name, tq.total_questions
  ORDER BY ass.created_at DESC
  LIMIT 10

我似乎无法使用查询生成器使其与子查询一起使用。如果没有子查询，我有这个，它可以为我提供评估标题和回答的问题数量:

Question.joins(:assessment => {:org_assessments => {:org => :users}}).joins(:answers)
                 .where(answers:{:user_id => params[:id]})
                 .distinct('answers.question_id').group(['assessments.name']).count()

我怎样才能像上面的原始 SQL 那样编写这个来包含子查询？

Answer 1

您可以将子查询作为字符串发送到 joins 方法:

subquery =
  TotalQuestion.
    joins(:assessments).
    group('assessments.id').
    select('assessments.id, COUNT(q.id) as total_questions').to_sql

Question.joins("(#{sub_query}) as tq on tq.id=ass.id")

您可以将它与查询的其他部分结合起来:

Question.
    joins(:assessment => {:org_assessments => {:org => :users}}).joins(:answers).
    joins("(#{sub_query}) as tq on tq.id=ass.id").
    where(answers:{:user_id => params[:id]}).
    distinct('answers.question_id').group(['assessments.name']).count()