Not tested, and kinda dodgy, but ..
class Post
scope :most_recently_active,
includes(:comments).order("max(comments.created_at, posts.created_at) DESC")
end
You should probably just go with the solution that you have right now. If
performance becomes a concern, I'd add an after_create hook on your Comment
class to update a datetime flag on the post itself, and then order on that
only.
Also re the below code:
- convention is to do "def self.blah" when defining a class method (or
use the class << self thing)
- self.comments.last will not return the most recent comment unless you
have a default scope ordering on your Comment class or relationship
On Thu, Feb 21, 2013 at 6:00 PM, Alex Bayley <[email protected]> wrote:
> I've got a Post class where I'm trying to display the most recently active
> posts. "Recently active" is based on the created_at timestamp of the
> latest comment on that post, or if there are no comments, then on the
> created_at timestamp of the post itself.
>
> Here's what I've got:
>
> def recent_activity
> self.comments.last ? self.comments.last.created_at : self.created_at
> end
>
> def Post.recently_active
> Post.all.sort do |a,b|
> b.recent_activity <=> a.recent_activity
> end
> end
>
> Is it possible to turn this into a named scope? I'm pretty sure order()
> won't take a calculated value. I know about using lambdas in scopes, too,
> but can't see how to combine that with sorting/ordering.
>
> Any ideas?
>
> A.
>
> --
> Alex "Skud" Bayley
> [email protected]
> http://growstuff.org/
> For personal stuff, please use [email protected]
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