from django.db.models import Sum, functions, Value


class RancherService:

    @staticmethod
    def get_total_used_weight(rancher, sale_item):
        return sale_item.objects.filter(
            transaction__rancher=rancher,
            transaction__transaction_status='success'
        ).aggregate(
            total_weight=functions.Coalesce(Sum('weight'), Value(0))
        )['total_weight']