如何按最近的帖子对用户进行排序？

Question

我有两个型号:User,并Post具有user_id柱(外键),和created_at列.

我想通过最新的帖子对用户进行排序.例如,如果:

user_id = 1, created 3 posts at: 17/05/2011, 19/05/2011, 21/05/2011
user_id = 2, created 1 post at: 22/05/2011
user_id = 3, created 2 posts at: 18/05/2011, 20/05/2011

结果应该是:

user_id = 2
user_id = 1
user_id = 3

你会如何在Rails 3中实现这一目标？

Answer 1

应该是这样的：

Post.select(:user_id).group(:user_id).order("created_at DESC")