Adds 'suppliers' field to Part serializer

- Number of supplier parts associated with the Part object

InvenTree/part/serializers.py

@@ -245,6 +245,14 @@ class PartSerializer(InvenTreeModelSerializer):
                 Decimal(0),
             )
         )
+
+        # Annotate with the number of 'suppliers'
+        queryset = queryset.annotate(
+            suppliers=Coalesce(
+                SubqueryCount('supplier_parts'),
+                Decimal(0),
+            ),
+        )
         
         return queryset
 
@@ -263,6 +271,7 @@ class PartSerializer(InvenTreeModelSerializer):
     ordering = serializers.FloatField(read_only=True)
     building = serializers.FloatField(read_only=True)
     stock_item_count = serializers.IntegerField(read_only=True)
+    suppliers = serializers.IntegerField(read_only=True)
 
     image = serializers.CharField(source='get_image_url', read_only=True)
     thumbnail = serializers.CharField(source='get_thumbnail_url', read_only=True)
@@ -308,6 +317,7 @@ class PartSerializer(InvenTreeModelSerializer):
             'salable',
             'starred',
             'stock_item_count',
+            'suppliers',
             'thumbnail',
             'trackable',
             'units',