has_many :through - Apply a limit to the join table

Question

I know I can apply a limit to the associations in a has_many :through, i.e.:

class Post
  has_many :commenters, through: :comments, uniq: true, limit: 10
end

This will return a maximum of 10 commenters. But what if I only want to know people who contributed the first 10 comments? (e.g. if there was a ping-pong comment thread, it would yield only 2 results). In other words, how do I limit the number of comments in this query?

Answer 1

Perhaps its better to separate the relation definition from the query you want to make.

class Post
  has_many :commenters, through: :comments

  def last_commenters
    comments.order('created_at DESC').limit(10).map{|c|c.commenter}.uniq
  end
end

Disclaimer: code not tested.