Eloquent One-to-Many OrderBy - laravel

Question

I'm working with Eloquent on a One-to-Many relationship.
I want to order my Users by using their last post DateTime (created_at) but I can't figure out how to make this work.
Table Users :
id | name
1 | John
2 | Doe
3 | Foo
4 | ...
Table Posts :
id | title | body | user_id | created_at
1 | Title 1| Body1 | 1 | 2014-03-06 14:00:00
2 | Title 2| Body2 | 1 | 2014-03-04 14:00:00
3 | Title 3| Body3 | 2 | 2014-03-03 14:00:00
4 | Title 4| Body4 | 3 | 2014-03-05 14:00:00
Example of final output desired :
name | title | created_at
John | Title 1 | 2014-03-06 14:00:00
Foo | Title 4 | 2014-03-05 14:00:00
Doe | Title 3 | 2014-03-03 14:00:00
The closer I could get was :
$users = User::with(['posts' => function($query){
$query->orderBy('created_at', 'desc');
}])->get();
But this code extracts all the posts for each user and I just want the last one.
Can you help me please? Thanks.
UPDATE : I finally found what I was looking for : Retrieve users' last post and sort the users in ascending order (of this last post's timestamp). Feel free to improve this query!
$users = DB::table('posts')
->join('users', 'posts.user_id', '=', 'users.id')
->select(DB::raw('posts.id, posts.user_id, MAX(created_at) as created_at'))
->groupBy('posts.user_id')
->orderBy('created_at', 'asc')
->get();

Answer 1

You may try this:
$users = User::with(array('posts' => function($query){
$query->orderBy('created_at', 'desc')->groupBy('user_id');
}))->get();
Update: You may try this:
$users = User::join('posts', 'users.id', '=', 'posts.user_id')
->orderBy('posts.created_at', 'desc')
->groupBy('posts.user_id')
->select('users.*', 'posts.created_at as postTime')
->get();
I've only selected created_at from posts table but you may add more fields in select like:
->select('users.*', 'posts.created_at as postTime', 'posts.updated_at as postUpTime', 'posts.id as pid', 'posts.title')

Answer 2

I believe you will either have to use usort() which is a little bit more complicated, or you can use joins, but with that method, you'd also lose the way Eloquent sets up the relations.
Using usort()...
private function cmp($a, $b)
{
if($a->posts->created_at == $b->posts->created_at) {
return 0;
}
return (strtotime($a->posts->created_at) < strtotime($b->posts->created_at)) ? -1 : 1;
}
$users = User::with(array('posts' => function($query){
$query->orderBy('created_at', 'desc')->groupBy('user_id')->first();
}))->get();
$users = usort($users, array($this, 'cmp'));
Or if you would prefer to use joins, I think this should work for you.
$users = DB::table('posts')
->select(DB::raw('MAX(`posts`.`created_at`) AS `created_at`, `user_id`, `users`.*'))
->orderBy('posts.created_at', 'desc')
->groupBy('posts.user_id')
->join('users', 'users.id', '=', 'posts.user_id')
->get();