catch attr exception for invalid SerializerMethodField #592

drf_spectacular/openapi.py

@@ -697,7 +697,14 @@ def _map_serializer_field(self, field, direction, bypass_extensions=False):
             return append_meta(content, meta)
 
         if isinstance(field, serializers.SerializerMethodField):
-            method = getattr(field.parent, field.method_name)
+            method = getattr(field.parent, field.method_name, None)
+            if method is None:
+                error(
+                    f'SerializerMethodField "{field.field_name}" is missing required method '
+                    f'"{field.method_name}". defaulting to "string".'
+                )
+                return append_meta(build_basic_type(OpenApiTypes.STR), meta)
+
             return append_meta(self._map_response_type_hint(method), meta)
 
         if isinstance(field, (serializers.BooleanField, serializers.NullBooleanField)):

tests/test_warnings.py

@@ -419,3 +419,17 @@ def view_func(request, format=None):
     generate_schema('x', view_function=view_func)
     stderr = capsys.readouterr().err
     assert 'invalid extension \'foo\'. vendor extensions must start with' in stderr
+
+
+def test_serializer_method_missing(capsys):
+    class XSerializer(serializers.Serializer):
+        some_field = serializers.SerializerMethodField()
+
+    @extend_schema(responses=XSerializer)
+    @api_view(['GET'])
+    def view_func(request):
+        pass  # pragma: no cover
+
+    generate_schema('x', view_function=view_func)
+    stderr = capsys.readouterr().err
+    assert 'SerializerMethodField "some_field" is missing required method "get_some_field"' in stderr