Improve speed of BomItem API queries

- Including the pricing information takes absolutely ages, takes too long!!

InvenTree/part/serializers.py

@@ -305,8 +305,13 @@ class BomItemSerializer(InvenTreeModelSerializer):
     price_range = serializers.CharField(read_only=True)
 
     quantity = serializers.FloatField()
+
+    part = serializers.PrimaryKeyRelatedField(queryset=Part.objects.filter(assembly=True))
     
     part_detail = PartBriefSerializer(source='part', many=False, read_only=True)
+
+    sub_part = serializers.PrimaryKeyRelatedField(queryset=Part.objects.filter(component=True))
+
     sub_part_detail = PartBriefSerializer(source='sub_part', many=False, read_only=True)
 
     validated = serializers.BooleanField(read_only=True, source='is_line_valid')
@@ -331,6 +336,7 @@ class BomItemSerializer(InvenTreeModelSerializer):
         queryset = queryset.prefetch_related('part')
         queryset = queryset.prefetch_related('part__category')
         queryset = queryset.prefetch_related('part__stock_items')
+
         queryset = queryset.prefetch_related('sub_part')
         queryset = queryset.prefetch_related('sub_part__category')
         queryset = queryset.prefetch_related('sub_part__stock_items')