Fix by_name() raising TypeError instead of returning None when nothing matches

fairgraph/kgobject.py

@@ -944,7 +944,7 @@ def by_name(
                         else:
                             cls._instance_lookup[key] = [instance]
             if match == "equals":
-                objects = cls._instance_lookup.get(name, None)
+                objects = cls._instance_lookup.get(name, [])
             elif match == "contains":
                 objects = []
                 for key, instances in cls._instance_lookup.items():

test/test_by_name.py

@@ -0,0 +1,73 @@
+# encoding: utf-8
+"""
+Tests of KGObject.by_name() using the local instance library
+(no Knowledge Graph connection needed).
+
+Regression test for https://github.com/HumanBrainProject/fairgraph/issues/130:
+by_name() raised TypeError ("object of type 'NoneType' has no len()")
+instead of returning None when no instance matched.
+"""
+
+from openminds.properties import Property
+
+from fairgraph.kgobject import KGObject
+
+import pytest
+
+
+class MockNamedTerm(KGObject):
+    """A mock controlled-term-like class with an empty instance library."""
+
+    type_ = "https://openminds.ebrains.eu/mock/MockNamedTerm"
+    default_space = "mock"
+    _instance_lookup = None
+    properties = [
+        Property("name", str, "https://openminds.ebrains.eu/vocab/name", multiple=False, required=False)
+    ]
+    reverse_properties = []
+
+    @classmethod
+    def instances(cls):
+        return []
+
+
+def test_by_name_no_match_returns_none():
+    assert MockNamedTerm.by_name("definitely not a term") is None
+
+
+def test_by_name_contains_no_match_returns_none():
+    assert MockNamedTerm.by_name("definitely not a term", match="contains") is None
+
+
+def test_by_name_match_found():
+    obj = MockNamedTerm(id="https://mock/kg/instances/00000000-0000-0000-0000-000000000001",
+                        space="mock", name="Rattus norvegicus")
+    MockNamedTerm._instance_lookup = {"Rattus norvegicus": [obj]}
+    try:
+        assert MockNamedTerm.by_name("Rattus norvegicus") is obj
+    finally:
+        MockNamedTerm._instance_lookup = None
+
+
+def test_by_name_multiple_matches_warns_and_returns_first():
+    obj1 = MockNamedTerm(id="https://mock/kg/instances/00000000-0000-0000-0000-000000000002",
+                         space="mock", name="Mus musculus")
+    obj2 = MockNamedTerm(id="https://mock/kg/instances/00000000-0000-0000-0000-000000000003",
+                         space="mock", name="Mus musculus")
+    MockNamedTerm._instance_lookup = {"Mus musculus": [obj1, obj2]}
+    try:
+        with pytest.warns(UserWarning, match="Multiple objects"):
+            result = MockNamedTerm.by_name("Mus musculus")
+        assert result is obj1
+        assert MockNamedTerm.by_name("Mus musculus", all=True) == [obj1, obj2]
+    finally:
+        MockNamedTerm._instance_lookup = None
+
+
+def test_by_name_invalid_match_raises_valueerror():
+    try:
+        MockNamedTerm.by_name("anything", match="approximate")
+    except ValueError as err:
+        assert "match" in str(err)
+    else:
+        raise AssertionError("ValueError not raised for invalid 'match' value")