Laravel 4.2：如何在Laravel中使用SUM的顺序

I have 3 tables:

Posts  
--id   
--post  
Points  
--id  
--user_id
--post_id  
--points     
User(disregard)
--id
--username

My models are like this.

Class Posts extends Eloquent {
   function points(){
       return $this->hasMany('points', 'post_id');
   }
}

Class Points extends Eloquent {
function posts() {
    return $this->belongsTo('posts', 'post_id');
}

How can I order it so that the returning results would be ordered by highest sum of points.I also need to know how I can get the sum of points per post.

Post_id | Post | Points<-- SumPoints
5       |Post1 | 100
3       |Post2 | 51
1       |Post3 | 44
4       |Post4 | 32

Here is my Code:

$homePosts = $posts->with("filters")
            ->with(array("points" => function($query) {
                    $query->select()->sum("points");
            }))->groupBy('id')
            ->orderByRaw('SUM(points) DESC')
            ->paginate(8);  

May I know how it would be solved by using query builder and/or model relationships

Eloquent way:

$posts = Post::leftJoin('points', 'points.post_id', '=', 'posts.id')
   ->selectRaw('posts.*, sum(points.points) as points_sum')
   ->orderBy('points_sum', 'desc')
   ->paginate(8);

The Query\Builder way is exactly the same, only the result won't be Eloquent models.

I think the following query-builder should get you started..

DB::table('posts')
    ->join('points', 'posts.id', '=', 'points.post_id')
    ->orderBy('sum(points)')
    ->groupBy('points.post_id')
    ->select('points.post_id', 'posts.post', 'sum(points.points) as points')
    ->paginate(8)
    ->get();