I'm using the Laravel-MongoDb package with a many to many relationship between "expeditions" and "subjects". Expeditions is MySql, Subjects is MongoDb. There is a pivot table "expedition_subject" that exists on one side, and within the Subjects collection, the Expedition Ids are stored in a "expedition_ids" field as an array.

"expedition_ids": [
     "1", "2", "3" 
  ] 

I'm trying to get the count for Subjects that are associated with an Expedition. For example:

$project = $this->project->findWith($id, ['expeditions.subjectsCountRelation']);

Projects have one to many relationship with Expeditions. Inside the Expedition Model, I have this:

        /**
	 * Return count through relationship
	 * @return mixed
	 */
	public function subjectsCountRelation ()
	{
		return $this->belongsToMany('Subject')
                            ->selectRaw('expedition_ids, count(*) as count')
                            ->groupBy('expedition_ids');
	}

	/**
	 * Get counts attribute
	 *
	 * @return int
	 */
	public function getSubjectsCountAttribute ()
	{
		return $this->subjectsCountRelation->first() ? 
                               $this->subjectsCountRelation->first()->count : 0;
	} 

Obviously it's not working due to the raw query being wrong. No error is generated. It simply returns nothing. Any ideas on how I might accomplish this?

Oh.... the above generates this MongoDB query

subjects.aggregate([
    {
        "$match": { "expedition_ids":  {  "$in":["1","2","3"] } }
    },
    {
         "$group":
         {
              "_id": { "expedition_ids":"$expedition_ids" },
              "expedition_ids": { "$last":"$expedition_ids" },
              "count(expedition_ids) as count(*)": { "$last":"$count(expedition_ids) as count(*)" }
        }
   }
])

I know the 3 Expeditions I have include 100 Subjects in each from the database seeding.