Implement get_subquery() for annotation of child object counts; Rename dcim.Site 'count_*' fields

netbox/utilities/utils.py

@@ -4,6 +4,7 @@ import datetime
 import json
 
 from django.core.serializers import serialize
+from django.db.models import Count, OuterRef, Subquery
 
 from dcim.constants import LENGTH_UNIT_CENTIMETER, LENGTH_UNIT_FOOT, LENGTH_UNIT_INCH, LENGTH_UNIT_METER
 
@@ -71,6 +72,23 @@ def model_names_to_filter_dict(names):
     }
 
 
+def get_subquery(model, field):
+    """
+    Return a Subquery suitable for annotating a child object count.
+    """
+    subquery = Subquery(
+        model.objects.filter(
+            **{field: OuterRef('pk')}
+        ).order_by().values(
+            field
+        ).annotate(
+            c=Count('*')
+        ).values('c')
+    )
+
+    return subquery
+
+
 def serialize_object(obj, extra=None):
     """
     Return a generic JSON representation of an object using Django's built-in serializer. (This is used for things like