diff --git a/src/caosdb/apiutils.py b/src/caosdb/apiutils.py
index a5a936c556dd065b56b60ff690baf9a1ce19a583..28e9a410f18a846493afda01ed27554d3878ac13 100644
--- a/src/caosdb/apiutils.py
+++ b/src/caosdb/apiutils.py
@@ -300,6 +300,7 @@ def compare_entities(old_entity: Entity, new_entity: Entity, compare_referenced_
                     # scalar reference
                     if isinstance(prop.value, Entity) and isinstance(matching[0].value, Entity):
                         # explicitely not recursive to prevent infinite recursion
+                        # TODO: why not use a recursion detection with a cache?
                         same_value = empty_diff(
                             prop.value, matching[0].value, compare_referenced_records=False)
                     # list of references