Failed to load data: Object of type HumanMessage is not JSON serializable

[ilangofman]

I know there were some other issues related to the JSON serilizer detailed on github. I tried using the latest versions with the fixes but any of the >0.2 versions of the redis langgraph checkpointers don't seem to work.

I keep getting the following error when trying to stream data from a graph execution:

redisvl.exceptions.RedisVLerror: failed to load data: Object of type HumanMessage is not JSON sesrializable

Pakage Versions

• langgraph: 1.0.2
• langchain-openai: 1.0.1
• langgraph-checkpoint: 3.0.0
• langgraph-checkpoint-redis: 0.2.1

Thank you for your help

[ilangofman]

Hi @bsbodden , thank you for looking at it and working quickly to fix it. After trying the newest release, I am still getting the same issue unfortunately. Here is the more detailed error trace:

09:13:25 redisvl.index.index ERROR    Error while loading data to Redis
Traceback (most recent call last):
  File "my_project/.venv/lib/python3.12/site-packages/redisvl/index/index.py", line 832, in load
    return self._storage.write(
           ^^^^^^^^^^^^^^^^^^^^
  File "my_project/.venv/lib/python3.12/site-packages/redisvl/index/storage.py", line 410, in write
    self._set(pipe, key, obj)
  File "my_project/.venv/lib/python3.12/site-packages/redisvl/index/storage.py", line 679, in _set
    client.json().set(key, "$", obj)
  File "my_project/.venv/lib/python3.12/site-packages/redis/commands/json/commands.py", line 243, in set
    pieces = [name, str(path), self._encode(obj)]
                               ^^^^^^^^^^^^^^^^^
  File "my_project/.venv/lib/python3.12/site-packages/redis/commands/json/__init__.py", line 102, in _encode
    return self.__encoder__.encode(obj)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/json/encoder.py", line 200, in encode
    chunks = self.iterencode(o, _one_shot=True)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/json/encoder.py", line 258, in iterencode
    return _iterencode(o, 0)
           ^^^^^^^^^^^^^^^^^
  File "/usr/lib64/python3.12/json/encoder.py", line 180, in default
    raise TypeError(f'Object of type {o.__class__.__name__} '
TypeError: Object of type HumanMessage is not JSON serializable

File "/usr/lib64/python3.12/concurrent/futures/_base.py", line 401, in __get_result
    raise self._exception
File "my_project/.venv/lib/python3.12/site-packages/langgraph/pregel/_executor.py", line 80, in done
    task.result()
File "/usr/lib64/python3.12/concurrent/futures/_base.py", line 449, in result
    return self.__get_result()
           ^^^^^^^^^^^^^^^^^^^
File "/usr/lib64/python3.12/concurrent/futures/_base.py", line 401, in __get_result
    raise self._exception
File "/usr/lib64/python3.12/concurrent/futures/thread.py", line 59, in run
    result = self.fn(*self.args, **self.kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "my_project/.venv/lib/python3.12/site-packages/langgraph/pregel/_loop.py", line 1031, in _checkpointer_put_after_previ
    cast(BaseCheckpointSaver, self.checkpointer).put(
File "my_project/.venv/lib/python3.12/site-packages/langgraph/checkpoint/redis/__init__.py", line 561, in put
    self.checkpoints_index.load(
File "my_project/.venv/lib/python3.12/site-packages/redisvl/index/index.py", line 849, in load
    raise RedisVLError(f"Failed to load data: {str(e)}") from e

redisvl.exceptions.RedisVLError: Failed to load data: Object of type HumanMessage is not JSON serializable

Package versions

• langgraph: 1.0.2
• langchain-openai: 1.0.1
• langgraph-checkpoint: 3.0.0
• langgraph-checkpoint-redis: 0.3.0
• langchain-core: 1.0.2

Thank you again for helping out with this

[abrookins]

Hi @ilangofman! Thanks for reporting. Are you able to share a minimum reproducible example we can use?

[demetere]

I am using langgraph-checkpoint-redis: 0.3.0 also face the same issue

[ilangofman]

After a lot of investigation and essentially trying to recreate the graph, I was able to reproduce this issue from a scratch graph. It is not really anything to do with the error message.

When I'm building my graph and I do builder.add_node(MyNodes.NodeA, node_a) where MyNodes.NodeA is a StrEnum and node_a is a simple method that returns a HumanMessage or AIMessage then I get this serialization error. If I just make the change in my code to builder.add_node("node_a", node_a) instead of using a StrEnum then I no longer get this error.