How to get sub-document size (count) in laravel mongodb jenssegers

Question

I want to fetch comment counts instead of fetching all comments in a single query, The below code I am using but getting the error

$answers = Answers::project([
    'comments'=>0, 
    'comments_count' => [
        '$size' => '$comments'
    ]])
    ->where('question_id',$request->question_id)
    ->get();

Error :- "message": "Unsupported projection option: comments_count: { $size: \"comments\" }",

Is $size aggregate support in jenssegers mongodb laravel package? if yes then that is the correct way to use it,

Thanks.

Answer 1

You can run a raw query with aggregate, check below query

$answers = Answers::raw(function($collection) use ($request) {
            return $collection->aggregate([
                [
                    '$match' => [
                        'question_id' => $request->question_id
                    ]
                ],
                [
                    '$project' => [
                        'answer'=>1,
                        'user'=>1,
                        'comment_count' => [
                            '$size' => [ 
                                '$ifNull'=> ['$comments', []] 
                            ] 
                        ]
                    ]
                ]
            ]);
        });

This is a working query in laravel 5.6 with jensseger mongodb.