Stringify orjson mapping keys after unstructure hooks

HISTORY.md

@@ -13,6 +13,8 @@ Our backwards-compatibility policy can be found [here](https://github.com/python
 
 ## NEXT
 
+- Ensure the orjson converter stringifies mapping keys after applying their unstructure hooks, including union and `Any` keys.
+
 - Dict unstructuring hook factories now inherit the converter's `omit_if_default` setting when `_cattrs_omit_if_default` is omitted. Explicit `True` or `False` values and per-attribute overrides retain their precedence.
   ([#238](https://github.com/python-attrs/cattrs/issues/238))
 - Support the [`frozendict`](https://docs.python.org/3.15/builtins/stdtypes.html#frozendict) built-in on Python 3.15+.

src/cattrs/preconf/orjson.py

@@ -80,7 +80,9 @@ def key_handler(v):
 
                 kh = converter.get_unstructure_hook(args[0])
                 if kh != identity:
-                    key_handler = kh
+
+                    def key_handler(v):
+                        return str(kh(v))
 
         return converter.gen_unstructure_mapping(
             cl, unstructure_to=unstructure_to, key_handler=key_handler

tests/test_preconf_orjson_keys.py

@@ -0,0 +1,60 @@
+"""Mapping keys remain strings after their configured unstructure hooks."""
+
+from base64 import b85encode
+from enum import Enum
+from typing import Any, Union
+
+import pytest
+from attrs import define
+
+orjson = pytest.importorskip("orjson")
+make_converter = pytest.importorskip("cattrs.preconf.orjson").make_converter
+
+
+@pytest.mark.parametrize("detailed_validation", [True, False])
+@pytest.mark.parametrize("key_type", [Union[str, int], str | int, Any, int])
+def test_mapping_keys_are_stringified(key_type, detailed_validation):
+    converter = make_converter(detailed_validation=detailed_validation)
+    data = {1: 7} if key_type is int else {1: 7, "second": 9}
+    expected = {str(key): value for key, value in data.items()}
+    target = dict[key_type, int]
+    assert converter.unstructure(data, unstructure_as=target) == expected
+    assert orjson.loads(converter.dumps(data, unstructure_as=target)) == expected
+
+
+def test_union_mapping_in_attrs_field():
+    @define
+    class Record:
+        entries: dict[Union[str, int], int]
+
+    converter = make_converter()
+    assert orjson.loads(converter.dumps(Record({1: 7}))) == {"entries": {"1": 7}}
+
+
+def test_string_enum_keys_keep_values():
+    class Key(str, Enum):
+        FIRST = "first"
+
+    converter = make_converter()
+    assert orjson.loads(
+        converter.dumps({Key.FIRST: 7}, unstructure_as=dict[Key, int])
+    ) == {"first": 7}
+
+
+def test_bytes_keys_keep_base85_hook():
+    converter = make_converter()
+    assert orjson.loads(
+        converter.dumps({b"key": 7}, unstructure_as=dict[bytes, int])
+    ) == {b85encode(b"key").decode("utf8"): 7}
+
+
+@pytest.mark.parametrize("hook_result", [42, "custom"])
+def test_custom_key_hook_is_applied_before_stringification(hook_result):
+    class Key:
+        pass
+
+    converter = make_converter()
+    converter.register_unstructure_hook(Key, lambda _: hook_result)
+    assert orjson.loads(converter.dumps({Key(): 7}, unstructure_as=dict[Key, int])) == {
+        str(hook_result): 7
+    }