Laravel Mongo GroupBy And count in an efficient manner - mongodb

Question

I have an authors collection that has a many-to-many relation to a posts collection. The posts collection has a category field which can be, for example, "Suspense", "Drama", "Action", etc.
I need to go through my entire posts collection and group by the category fields and also have the associated counts.
This is what I have so far:
$authors = Author::where('active', true)->get();
foreach ($authors as $author){
foreach ($author->posts()->groupBy('category')->get() as $data){
// Do some logic
}
}
Basically the output I am expecting is an array with category as keys and the counts as a value. So if I do $a['Drama'] it gives me count of how many times that author wrote a post with that category.
I can probably figure it out by working in my loop logic above but it does not look very efficient. Should I look at aggregation? If so can someone get me started?

Answer 1

Try this:
use Illuminate\Support\Collection;
use Illuminate\Support\Facades\DB;
$authors = DB::collection('authors')
->where('active', true)
->get();
// Laravel >= 5.3 would return collection instead of plain array
$authors = is_array($authors) ? Collection::make($authors) : $authors;
$authors->map(function ($author) {
return $author
->posts()
->groupBy('category')
->get()
->map(function ($collection) {
return $collection->count();
});
});