From f4021dc664b2b311ee217b6fa140ecef67af50a0 Mon Sep 17 00:00:00 2001
From: Sylphia Windy <admin@sylphia.org>
Date: Mon, 8 Sep 2025 18:34:25 +0800
Subject: [PATCH] fix: generic type args should be serialized for
 de-serialization, closes #6102

---
 .../langgraph/checkpoint/serde/jsonplus.py    | 59 ++++++++++++++++++-
 libs/checkpoint/tests/test_jsonplus.py        | 31 ++++++++++
 2 files changed, 88 insertions(+), 2 deletions(-)

diff --git a/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py b/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py
index 45980c64eb..4cd6a6bb0f 100644
--- a/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py
+++ b/libs/checkpoint/langgraph/checkpoint/serde/jsonplus.py
@@ -255,8 +255,57 @@ def loads_typed(self, data: tuple[str, bytes]) -> Any:
 EXT_NUMPY_ARRAY = 6
 
 
+def _try_get_pydantic_v2_generic_type_info(
+    pydantic_type: Any,
+) -> tuple[str, dict]:
+    from collections import defaultdict
+
+    info_dict: dict[tuple[str, str], Any] = defaultdict(list)
+
+    generics = getattr(pydantic_type, "__pydantic_generic_metadata__", {})
+    origin_class = generics.get("origin")
+    type_args = generics.get("args", [])
+
+    if not origin_class or not type_args:
+        return "", info_dict
+
+    for arg in type_args:
+        child_generics = getattr(arg, "__pydantic_generic_metadata__", {})
+
+        if child_generics.get("origin"):
+            origin_cls_name, sub_dict = _try_get_pydantic_v2_generic_type_info(arg)
+            info_dict[(origin_class.__module__, origin_cls_name)].append(sub_dict)
+        else:
+            info_dict[(origin_class.__module__, origin_class.__name__)].append(
+                (arg.__module__, arg.__name__)
+            )
+
+    return origin_class.__name__, info_dict
+
+
+def _build_generic_pydantic_v2_type(
+    module_name: str, orign_cls_name: str, type_info_dict: dict
+) -> Any:
+    generic_type_arg_info = type_info_dict[(module_name, orign_cls_name)]
+    origin_cls = getattr(importlib.import_module(module_name), orign_cls_name)
+    generic_type_args = []
+    for arg_info in generic_type_arg_info:
+        if isinstance(arg_info, dict):
+            m, c = next(iter(arg_info))
+            type_arg = _build_generic_pydantic_v2_type(m, c, arg_info)
+        else:
+            type_arg = getattr(importlib.import_module(arg_info[0]), arg_info[1])
+        generic_type_args.append(type_arg)
+    cls = origin_cls.__class_getitem__(tuple(generic_type_args))
+
+    return cls
+
+
 def _msgpack_default(obj: Any) -> str | ormsgpack.Ext:
     if hasattr(obj, "model_dump") and callable(obj.model_dump):  # pydantic v2
+        origin_cls_name, generic_type_info = _try_get_pydantic_v2_generic_type_info(
+            obj.__class__
+        )
         return ormsgpack.Ext(
             EXT_PYDANTIC_V2,
             _msgpack_enc(
@@ -265,6 +314,8 @@ def _msgpack_default(obj: Any) -> str | ormsgpack.Ext:
                     obj.__class__.__name__,
                     obj.model_dump(),
                     "model_validate_json",
+                    origin_cls_name,
+                    generic_type_info,
                 ),
             ),
         )
@@ -544,8 +595,12 @@ def _msgpack_ext_hook(code: int, data: bytes) -> Any:
             tup = ormsgpack.unpackb(
                 data, ext_hook=_msgpack_ext_hook, option=ormsgpack.OPT_NON_STR_KEYS
             )
-            # module, name, kwargs, method
-            cls = getattr(importlib.import_module(tup[0]), tup[1])
+            # module, name, kwargs, method, generic_type_info, origin_cls_name
+            if len(tup) > 4 and tup[4] and isinstance(tup[5], dict) and len(tup[5]) > 0:
+                # serialized data has generic type info
+                cls = _build_generic_pydantic_v2_type(tup[0], tup[4], tup[5])
+            else:
+                cls = getattr(importlib.import_module(tup[0]), tup[1])
             try:
                 return cls(**tup[2])
             except Exception:
diff --git a/libs/checkpoint/tests/test_jsonplus.py b/libs/checkpoint/tests/test_jsonplus.py
index 348492ae0b..4192c163b8 100644
--- a/libs/checkpoint/tests/test_jsonplus.py
+++ b/libs/checkpoint/tests/test_jsonplus.py
@@ -8,6 +8,7 @@
 from decimal import Decimal
 from enum import Enum
 from ipaddress import IPv4Address
+from typing import Generic, TypeVar
 from zoneinfo import ZoneInfo
 
 import dataclasses_json
@@ -24,6 +25,14 @@
 )
 from langgraph.store.base import Item
 
+TInner = TypeVar("TInner", bound=BaseModel)
+
+
+class MyPydanticGeneric(BaseModel, Generic[TInner]):
+    foo: str
+    bar: int
+    inner: TInner
+
 
 class InnerPydantic(BaseModel):
     hello: str
@@ -469,3 +478,25 @@ def test_serde_jsonplus_pandas_series(series: pd.Series) -> None:
     result = serde.loads_typed(dumped)
 
     assert result.equals(series)
+
+
+def test_serde_jsonplus_with_pydantic_generic() -> None:
+    instance = MyPydanticGeneric[MyPydanticGeneric[InnerPydantic]](
+        foo="foo",
+        bar=1,
+        inner=MyPydanticGeneric[InnerPydantic](
+            foo="inner-foo", bar=2, inner=InnerPydantic(hello="hello")
+        ),
+    )
+
+    serde = JsonPlusSerializer()
+    dumped = serde.dumps_typed(instance)
+    assert dumped[0] == "msgpack"
+    result = serde.loads_typed(dumped)
+    assert instance == result
+
+    # json mode is not affected by the fix
+    serde = JsonPlusSerializer(__unpack_ext_hook__=_msgpack_ext_hook_to_json)
+
+    json_result = serde.loads_typed(dumped)
+    assert json_result == instance.model_dump()