fix(filters): serialize reference counts for GraphQL aggregation

test/collection/test_filter.py

@@ -12,10 +12,32 @@
     _FilterValue,
     _Operator,
 )
-from weaviate.collections.filters import _FilterToGRPC
+from weaviate.collections.filters import _FilterToGRPC, _FilterToREST
 from weaviate.proto.v1 import base_pb2
 
 
+@pytest.mark.parametrize("compound", [False, True])
+def test_graphql_reference_count_filter(compound: bool) -> None:
+    """Serialize reference-count targets for direct and compound GraphQL filters."""
+    ref_filter = wvc.query.Filter.by_ref_count("ref").greater_than(0)
+    expected_ref = {
+        "operator": "GreaterThan",
+        "path": ["ref"],
+        "valueInt": 0,
+    }
+    if compound:
+        combined = ref_filter & wvc.query.Filter.by_property("name").equal("Berlin")
+        assert _FilterToREST.convert(combined) == {
+            "operator": "And",
+            "operands": [
+                expected_ref,
+                {"operator": "Equal", "path": ["name"], "valueText": "Berlin"},
+            ],
+        }
+    else:
+        assert _FilterToREST.convert(ref_filter) == expected_ref
+
+
 def test_empty_input_contains_any() -> None:
     with pytest.raises(weaviate.exceptions.WeaviateInvalidInputError):
         wvc.query.Filter.by_id().contains_any([])

weaviate/collections/filters.py

@@ -205,6 +205,8 @@ def __value_filter(weav_filter: _FilterValue) -> Dict[str, Any]:
     def __to_path(target: _FilterTargets) -> List[str]:
         if isinstance(target, str):
             return [target]
+        elif isinstance(target, _CountRef):
+            return [target.link_on]
         elif isinstance(target, _SingleTargetRef):
             raise WeaviateInvalidInputError(
                 "Cannot use Filter.by_ref() in the aggregate API currently. Instead use Filter.by_ref_multi_target() and specify the target collection explicitly."