Using Pydantic state with aliased fields

[eyurtsev]

Privileged issue

• I am a LangChain maintainer, or was asked directly by a LangChain maintainer to create an issue here.

Issue Content

MRE

from pydantic import BaseModel, Field
from langgraph.graph import StateGraph

class Foo(BaseModel):
    foo: str = Field(alias='bar')

# Define a new graph
graph_builder = StateGraph(
    Foo
)


def node(foo: Foo):
    print(foo)
    return None

# Add the node to the graph
graph_builder.add_node("node", node)
# Set the entrypoint as `call_model`
graph_builder.add_edge("__start__", "node")

# Compile the workflow into an executable graph
graph = graph_builder.compile()


graph.invoke({'bar': 'hello'})

Expected behavior

The alias should be respected and the field foo should be only updateable by alias.

Observed behavior

Validation error.

Context

• Mostly a problem for IO boundaries (since that's where I actually use pydantic models)
• alias is needed in some cases to avoid name collisions (e.g., schema field is already taken by pydantic)

[FrancisGajitos]

Hi @eyurtsev,

I've looked into the issue and I'm interested in working on fixing it right away. Please let me know if there's anything further I should know about it.

Thanks!