Update queryset annotation for StockItem

- Query time reduced from 4.1 to 3.5s (for sample data)

InvenTree/stock/serializers.py

@@ -9,9 +9,12 @@ from .models import StockItemTracking
 from .models import StockItemAttachment
 from .models import StockItemTestResult
 
-from django.db.models import Sum, Count
 from django.db.models.functions import Coalesce
 
+from sql_util.utils import SubquerySum, SubqueryCount
+
+from decimal import Decimal
+
 from company.serializers import SupplierPartSerializer
 from part.serializers import PartBriefSerializer
 from InvenTree.serializers import UserSerializerBrief, InvenTreeModelSerializer
@@ -90,11 +93,18 @@ class StockItemSerializer(InvenTreeModelSerializer):
         performing database queries as efficiently as possible.
         """
 
+        # Annotate the queryset with the total allocated to sales orders
         queryset = queryset.annotate(
             allocated=Coalesce(
-                Sum('sales_order_allocations__quantity', distinct=True), 0) + Coalesce(
-                Sum('allocations__quantity', distinct=True), 0),
-            tracking_items=Count('tracking_info'),
+                SubquerySum('sales_order_allocations__quantity'), Decimal(0)
+            ) + Coalesce(
+                SubquerySum('allocations__quantity'), Decimal(0)
+            )
+        )
+
+        # Annotate the queryset with the number of tracking items
+        queryset = queryset.annotate(
+            tracking_items=SubqueryCount('tracking_info')
         )
 
         return queryset