Laravel 5.8 How to order by sum of pivot table value in foreach? - laravel

Question

I have the following tables:
parts:
id | name
1 | Lock
2 | Light
shelves:
id | name
1 | 1A
2 | 1B
part_shelf
id | part_id | shelf_id | stock
1 | 1 | 1 | 5
2 | 1 | 2 | 10
3 | 2 | 1 | 4
The relations:
In Part model:
public function shelves()
{
return $this->belongsToMany( Shelf::class )->withPivot( 'stock' );
}
In shelf model:
public function parts()
{
return $this->belongsToMany(Part::class)->withPivot('stock');
}
What I would like to do is order all the parts based on the total stock of the pivot table.
What I have tried is the following:
$parts = Part::all(); // This is inside controller
#foreach($parts->shelves()->orderBy('pivot_stock', 'desc') as $part)
#foreach($parts->shelves()->orderBy('part_shelf.stock', 'desc') as $part)
I do know that I can get the total stock for individual parts with:
$part->shelves()->sum('stock')
I just don't know how to approach it for all parts in the foreach-loop.
Also looked at other questions but that didn't really help:
How to order by pivot table data in Laravel's Eloquent ORM
Order by pivot table created_at in Laravel
Laravel 5.4 Eloquent SUM and ORDER BY pivot table column I think is the closest to what I'm looking for

Answer 1

I had similar problem. I had three tables. Players (in my code "Igrac"), tournaments(in my code "Turnir_Piramida"), and players_tournaments pivot table(in my code "Nastup_piramida"). In pivot table was also column point for points for each player in each tournament. And i needed to summarize points from each player and then sort table by sum of points.
I manage to do that with third link you posted. You can see my solution on this link