Fixes for aggregation issues

- Ensure that "distinct=True" is set!
- ARRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

InvenTree/part/serializers.py

@@ -10,6 +10,12 @@ from .models import PartCategory
 from .models import BomItem
 from .models import PartParameter, PartParameterTemplate
 
+from decimal import Decimal
+
+from django.db.models import Q, F, Sum, Count
+from django.db.models.functions import Coalesce
+
+from InvenTree.status_codes import StockStatus, OrderStatus, BuildStatus
 from InvenTree.serializers import InvenTreeModelSerializer
 
 
@@ -78,24 +84,77 @@ class PartSerializer(InvenTreeModelSerializer):
     Used when displaying all details of a single component.
     """
 
-    allocated_stock = serializers.FloatField(source='allocation_count', read_only=True)
-    bom_items = serializers.IntegerField(source='bom_count', read_only=True)
-    building = serializers.FloatField(source='quantity_being_built', read_only=False)
-    category_name = serializers.CharField(source='category_path', read_only=True)
-    image = serializers.CharField(source='get_image_url', read_only=True)
-    on_order = serializers.FloatField(read_only=True)
-    thumbnail = serializers.CharField(source='get_thumbnail_url', read_only=True)
-    url = serializers.CharField(source='get_absolute_url', read_only=True)
-    used_in = serializers.IntegerField(source='used_in_count', read_only=True)
+    @staticmethod
+    def prefetch_queryset(queryset):
+        return queryset.prefetch_related(
+            'category',
+            'stock_items',
+            'bom_items',
+            'builds',
+            'supplier_parts',
+            'supplier_parts__purchase_order_line_items',
+            'supplier_parts__purcahes_order_line_items__order'
+        )
 
     @staticmethod
-    def setup_eager_loading(queryset):
-        queryset = queryset.prefetch_related('category')
-        queryset = queryset.prefetch_related('stock_items')
-        queryset = queryset.prefetch_related('bom_items')
-        queryset = queryset.prefetch_related('builds')
+    def annotate_queryset(queryset):
+        """
+        Add some extra annotations to the queryset, 
+        performing database queries as efficiently as possible,
+        to reduce database trips.
+        """
+
+        # Filter to limit stock items to "available"
+        stock_filter = Q(stock_items__status__in=StockStatus.AVAILABLE_CODES)
+
+        # Filter to limit orders to "open"
+        order_filter = Q(supplier_parts__purchase_order_line_items__order__status__in=OrderStatus.OPEN)
+
+        # Filter to limit builds to "active"
+        build_filter = Q(builds__status__in=BuildStatus.ACTIVE_CODES)
+
+        # Annotate the number total stock count
+        queryset = queryset.annotate(
+            in_stock=Coalesce(Sum('stock_items__quantity', filter=stock_filter, distinct=True), Decimal(0))
+        )
+
+        # Annotate the number of parts "on order"
+        # Total "on order" parts = "Quantity" - "Received" for each active purchase order
+        queryset = queryset.annotate(
+            ordering=Coalesce(Sum(
+                'supplier_parts__purchase_order_line_items__quantity',
+                filter=order_filter,
+                distinct=True
+            ), Decimal(0)) - Coalesce(Sum(
+                'supplier_parts__purchase_order_line_items__received',
+                filter=order_filter,
+                distinct=True
+            ), Decimal(0))
+        )
+
+        # Annotate number of parts being build
+        queryset = queryset.annotate(
+            building=Coalesce(
+                Sum('builds__quantity', filter=build_filter, distinct=True), Decimal(0)
+            )
+        )
+        
         return queryset
 
+    in_stock = serializers.FloatField(read_only=True)
+    ordering = serializers.FloatField(read_only=True)
+    building = serializers.FloatField(read_only=True)
+
+    #allocated_stock = serializers.FloatField(source='allocation_count', read_only=True)
+    #bom_items = serializers.IntegerField(source='bom_count', read_only=True)
+    #building = serializers.FloatField(source='quantity_being_built', read_only=False)
+    #category_name = serializers.CharField(source='category_path', read_only=True)
+    image = serializers.CharField(source='get_image_url', read_only=True)
+    #on_order = serializers.FloatField(read_only=True)
+    thumbnail = serializers.CharField(source='get_thumbnail_url', read_only=True)
+    url = serializers.CharField(source='get_absolute_url', read_only=True)
+    #used_in = serializers.IntegerField(source='used_in_count', read_only=True)
+
     # TODO - Include a 'category_detail' field which serializers the category object
 
     class Meta:
@@ -103,31 +162,34 @@ class PartSerializer(InvenTreeModelSerializer):
         partial = True
         fields = [
             'active',
-            'allocated_stock',
+            #'allocated_stock',
             'assembly',
-            'bom_items',
-            'building',
+            #'bom_items',
+            #'building',
             'category',
-            'category_name',
+            #'category_name',
             'component',
             'description',
             'full_name',
             'image',
+            'in_stock',
+            'ordering',
+            'building',
             'IPN',
             'is_template',
             'keywords',
             'link',
             'name',
             'notes',
-            'on_order',
+            #'on_order',
             'pk',
             'purchaseable',
             'salable',
             'thumbnail',
             'trackable',
-            'total_stock',
+            #'total_stock',
             'units',
-            'used_in',
+            #'used_in',
             'url',  # Link to the part detail page
             'variant_of',
             'virtual',