php - Laravel OrderBy relationship count

Question

I'm trying to get the most popular hackathons which requires ordering by the respective hackathon's partipants->count(). Sorry if that's a little difficult to understand.

I have a database with the following format:

hackathons
    id
    name
    ...

hackathon_user
    hackathon_id
    user_id

users
    id
    name

The Hackathon model is:

class Hackathon extends Eloquent {
    protected $fillable = ['name', 'begins', 'ends', 'description'];

    protected $table = 'hackathons';

    public function owner()
    {
        return $this->belongsToMany('User', 'hackathon_owner');
    }

    public function participants()
    {
        return $this->belongsToMany('User');
    }

    public function type()
    {
        return $this->belongsToMany('Type');
    }
}

And HackathonParticipant is defined as:

class HackathonParticipant extends Eloquent {

    protected $fillable = ['hackathon_id', 'user_id'];

    protected $table = 'hackathon_user';

    public function user()
    {
        return $this->belongsTo('User', 'user_id');
    }

    public function hackathon()
    {
        return $this->belongsTo('Hackathon', 'hackathon_id');
    }
}

I've tried Hackathon::orderBy(HackathonParticipant::find($this->id)->count(), 'DESC')->take(5)->get()); but I feel like I made a big mistake (possibly the $this->id), because it doesn't work at all.

How would I go about trying to get the most popular hackathons which is based on the highest number of related hackathonParticipants?

Answer 1

This works for me in Laravel 5.3, using your example:

Hackathon::withCount('participants')->orderBy('participants_count', 'desc')->paginate(10); 

This way it is ordered on the query and the pagination works nicely.