fix: evaluate only the requested metadata comparator

datamind/capabilities/kb/filters.py

@@ -52,16 +52,26 @@ def matches_metadata(metadata: dict[str, Any], where: dict[str, Any] | None) ->
             continue
         op, value = next(iter(expected.items()))
         try:
-            ok = {
-                "$eq": actual == value,
-                "$ne": actual != value,
-                "$in": actual in value,
-                "$nin": actual not in value,
-                "$gt": actual > value,
-                "$gte": actual >= value,
-                "$lt": actual < value,
-                "$lte": actual <= value,
-            }[op]
+            # Dispatch before evaluating the operation. Building a mapping of
+            # boolean results evaluates every comparator, so an unrelated
+            # ordering or membership operation can turn a valid match into a
+            # false negative (for example, 42 == 42 also evaluates 42 in 42).
+            if op == "$eq":
+                ok = actual == value
+            elif op == "$ne":
+                ok = actual != value
+            elif op == "$in":
+                ok = actual in value
+            elif op == "$nin":
+                ok = actual not in value
+            elif op == "$gt":
+                ok = actual > value
+            elif op == "$gte":
+                ok = actual >= value
+            elif op == "$lt":
+                ok = actual < value
+            else:
+                ok = actual <= value
         except (TypeError, KeyError):
             ok = False
         if not ok:

datamind/tests/test_filters.py

@@ -0,0 +1,43 @@
+"""Metadata comparator dispatch tests."""
+from __future__ import annotations
+
+import pytest
+
+from datamind.capabilities.kb.filters import matches_metadata
+
+
+@pytest.mark.parametrize(
+    ("actual", "operator", "expected", "matched"),
+    [
+        (42, "$eq", 42, True),
+        (42, "$eq", 41, False),
+        (42, "$ne", 41, True),
+        (42, "$ne", 42, False),
+        ("a", "$in", ["a", "b"], True),
+        ("c", "$in", ["a", "b"], False),
+        ("c", "$nin", ["a", "b"], True),
+        ("a", "$nin", ["a", "b"], False),
+        (42, "$gt", 40, True),
+        (42, "$gt", 42, False),
+        (42, "$gte", 42, True),
+        (42, "$gte", 43, False),
+        (40, "$lt", 42, True),
+        (42, "$lt", 42, False),
+        (42, "$lte", 42, True),
+        (43, "$lte", 42, False),
+    ],
+)
+def test_matches_metadata_dispatches_only_the_requested_comparator(
+    actual, operator, expected, matched,
+):
+    assert matches_metadata({"value": actual}, {"value": {operator: expected}}) is matched
+
+
+def test_nested_boolean_filters_keep_comparator_dispatch_local():
+    assert matches_metadata(
+        {"age": 42, "tag": "a"},
+        {"$and": [
+            {"age": {"$gt": 40}},
+            {"tag": {"$in": ["a", "b"]}},
+        ]},
+    )