How do I query an association for non-unique values of a field with SQL/ActiveRecord?

Honestly I'm not even sure how to describe it in a single sentence, so that title might be way off. Here's what I'm trying to do:

I've got a fairly simple model. User -> Stories -> Comments. That is, a User has_many Stories, and a Story has_many Comments.

What I'm trying to do is only return the stories that:

• Have comments
• Were either created by the current user or have been commented on by the current_user
• But not if the开发者_运维知识库 current user is the only user to comment on it

What I have so far is:

Story.includes(:comments).where("stories.user_id = ? OR comments.user_id = ?", current_user.id, current_user.id)

But I have no idea how to do the last condition in SQL. The only thing I could do was use Enumerable methods.

@stories.reject! { |story| story.comments.collect(&:user_id).all? { |user_id| user_id == current_user.id }}

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Sounds like you want to have a nested subquery, something like

Story.includes(:comments).where("stories.user_id = ? OR comments.user_id = ?) 
    and exists (select 'x' from comments c2 where c2.story_id = stories.id 
    and c2.user_id != ?)",
  current_user.id, current_user.id, current_user.id)