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fix(langgraph): fix PostgresSaver crashing when loading older checkpoints (#6162)

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### Description

https://github.com/langchain-ai/langgraph/issues/6137 and
https://github.com/langchain-ai/langgraph/issues/5677 reported issues
where older checkpoints read by AsyncPostgresSaver/PostgresSaver from
`langgraph-checkpoint-postgres==2.0.19` fail to read channel values,
throwing `NoneType object is not a mapping`. This was due to a bug in
how `channel_values` is assembled:
```python
"channel_values": {
    **value["checkpoint"].get("channel_values"),  # <--- if channel_values doesn't exist (old checkpoint), **None errors
    **self._load_blobs(value["channel_values"]),
},
```
This bug was observed for checkpoints generated by
`langgraph-checkpoint-postgres<=2.0.19`.

Fixed by providing a fallback to
`value["checkpoint"].get("channel_values")`:
```python
**value["checkpoint"],
"channel_values": {
    **(
        value["checkpoint"].get("channel_values") or {}
    ),  # 'or {}' needed for backwards compat with v3 checkpoints and below, as v4 introduced channel_values key
    **self._load_blobs(value["channel_values"]),
},
```

### Tests
Added test for AsyncPostgresSaver and test for PostgresSaver, using
monkeypatch to remove `channel_values` before CheckpointTuple is
assembled in `_load_checkpoint_tuple`.

### Solves
https://github.com/langchain-ai/langgraph/issues/6137 and
https://github.com/langchain-ai/langgraph/issues/5677

---------

Co-authored-by: Shahrukh Shaik <144558473+shahrukh-shaik@users.noreply.github.com>
This commit is contained in:
Caspar Broekhuizen
2025-09-17 17:50:39 -07:00
committed by GitHub
co-authored by Shahrukh Shaik
parent 8dc4465d05
commit f0fced262a
4 changed files with 63 additions and 2 deletions
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libs/checkpoint-postgres/langgraph/checkpoint/postgres/__init__.py
+1 -1
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@@ -450,7 +450,7 @@ class PostgresSaver(BasePostgresSaver):
{
**value["checkpoint"],
"channel_values": {
**value["checkpoint"].get("channel_values"),
**(value["checkpoint"].get("channel_values") or {}),
**self._load_blobs(value["channel_values"]),
},
},
libs/checkpoint-postgres/langgraph/checkpoint/postgres/aio.py
+1 -1
View File
@@ -409,7 +409,7 @@ class AsyncPostgresSaver(BasePostgresSaver):
{
**value["checkpoint"],
"channel_values": {
**value["checkpoint"].get("channel_values"),
**(value["checkpoint"].get("channel_values") or {}),
**self._load_blobs(value["channel_values"]),
},
},