Question

如何编写一个给出以下结果的查询：

https://stackoverflow.com/users/611696/hopstream?tab=tags

鉴于这些模型和关系：

User:
    has_many: questions
    has_many: answers

Questions:
    belongs_to: user
    has_and_belongs_to_many: tags
    has_many: answers

Answers:
    belongs_to: user
    belongs_to: question

Tags:
    has_and_belongs_to_many: questions

应该是在用户模型中，对吗？...

class User < MyModel
   def topics
      # get user's questions' topics
      # get user's answers' questions' topics
      # merge and remove duplicates
      # sort by user's activity on topic (group by of questions and answers user has posted where the question had that tag)
   end
end

或者有更简单的方法来实现这一目标吗？

Answer 1

在我看来，任何形式的ORM都有助于根据一些（足够简单的）标准和遍历关联来检索记录。对于更复杂的报告这样的东西，不要犹豫使用纯SQL，它更适合这个。

下面是未经测试的，但应指向正确的方向：

class User < MyModel
  def topics
    connection.execute <<SQL
      SELECT tag, count(*)
      FROM questions_tags
      WHERE question_id IN (
        SELECT id
        FROM questions
        WHERE user_id = #{id}
        UNION ALL
        SELECT questions.id
        FROM questions JOIN answers ON (question.id = answers.question_id)
        WHERE answers.user_id = #{id}
      )
      GROUP BY tag;
    SQL
  end
end

在rails中Stackoverflow用户的标签查询？

1 个答案: