Laravel eloquent restrict withCount with whereHas or another - php

Question

I have 3 models Supplier, Purchase and PurchaseDetail.
To join the Supplier model with PurchaseDetail through Purchase I have created a hasManyThrough relation.
hasManyThrough inside Supplier model:
public function detail_purchases(){
return $this->hasManyThrough(PurchaseDetail::class, Purchase::class);
}
The relationship works well and I can count the quantities purchased from sellers as follows:
$collectors = Supplier::withCount(['detail_purchases as qty_sold' => function($query) {
return $query->select(\DB::raw('SUM(qty)'))
->where('unit', '=', 'kg');
}])
->where('supplier_type','=','persona_natural')
->orderBy('qty_sold','desc')
->get();
SQL Query output:
select `suppliers`.*, (
select SUM(qty)
from `purchase_details`
inner join `purchases` on `purchases`.`id` = `purchase_details`.`purchase_id`
where `suppliers`.`id` = `purchases`.`supplier_id`
and `unit` = 'kg'
and `purchases`.`deleted_at` is null
) as `qty_sold`
from `suppliers`
where `supplier_type` = 'persona_natural'
order by `qty_sold` desc;
Output rows:
My problem is that this query is bringing me sellers that I did not make purchases from them, I don't know why they infiltrate the query if it is assumed that the hasManyThrough relationship only joins those who are registered in Purchase or made purchases from them.
Also the Supplier model has another relation called purchases:
public function purchases() {
return $this->hasMany(Purchase::class, 'supplier_id');
}
And the model Purchase has a relation hasMany with PurchaseDetail :
public function details(){
return $this->hasMany(PurchaseDetail::class, 'purchase_id');
}
Updated
Using whereHas now I can get all the suppliers that I did purchases however the qty_sold is not appearing in the results:
$collectors = Supplier::whereHas('purchases', function($query){
$query->withCount(['details as qty_sold' => function($query){
$query->select(\DB::raw('SUM(qty)'))
->where('unit', '=', $this->unit);
}]);
})
->where('supplier_type','=','persona_natural')
->get();
This selection is important because I want to know how many kgs of all products I purchased.

Answer 1

Thanks #Tony
In your updated query can you move the withCount out of the subquery? So you would have Supplier::withCount(...)->whereHas('purchases')..
Ok, I fixed it, adding first the whereHas directive the I used the hasManyThrough
relation with withCount. Of this way only suppliers that has purchases are selection.
$collectors = Supplier::whereHas('purchases')
->withCount([
'detail_purchases as qty_sold' => function($query){
$query->select(\DB::raw('SUM(qty)'))
->where('unit', '=', 'kg');
}
])
->where('supplier_type','=', 'persona_natural')
->get();