langgraph: handle pydantic updates consistently in Command

libs/langgraph/langgraph/graph/state.py

@@ -764,14 +764,14 @@ class CompiledStateGraph(CompiledGraph):
                         updates.extend(_get_updates(i) or ())
                 return updates
             elif (t := type(input)) and get_type_hints(t):
-                # Pydantic v2
+                # Pydantic v1
                 if isinstance(input, BaseModelV1):
                     keep: Optional[set[str]] = input.__fields_set__
                     defaults = {k: v.default for k, v in t.__fields__.items()}
+                # Pydantic v2
                 elif isinstance(input, BaseModel):
                     keep = input.model_fields_set
                     defaults = {k: v.default for k, v in input.model_fields.items()}
-                # Pydantic v1
                 else:
                     keep = None
                     defaults = {}

libs/langgraph/langgraph/types.py

@@ -20,6 +20,8 @@ from typing import (
 )
 
 from langchain_core.runnables import Runnable, RunnableConfig
+from pydantic import BaseModel
+from pydantic.v1 import BaseModel as BaseModelV1
 from typing_extensions import Self
 
 from langgraph.checkpoint.base import BaseCheckpointSaver, CheckpointMetadata
@@ -69,6 +71,11 @@ else:
     _DC_KWARGS = {"frozen": True}
 
 
+# NOTE: this is redefined here separately from langgraph.constants
+# to avoid a circular import
+MISSING = object()
+
+
 def default_retry_on(exc: Exception) -> bool:
     import httpx
     import requests
@@ -318,7 +325,28 @@ class Command(Generic[N], ToolOutputMixin):
         ):
             return self.update
         elif hints := get_type_hints(type(self.update)):
-            return [(k, getattr(self.update, k)) for k in hints]
+            # Pydantic v1
+            if isinstance(self.update, BaseModelV1):
+                keep: Optional[set[str]] = self.update.__fields_set__
+                defaults = {k: v.default for k, v in self.update.__fields__.items()}
+            # Pydantic v2
+            elif isinstance(self.update, BaseModel):
+                keep = self.update.model_fields_set
+                defaults = {k: v.default for k, v in self.update.model_fields.items()}
+            else:
+                keep = None
+                defaults = {}
+
+            return [
+                (k, value)
+                for k in hints
+                if (value := getattr(self.update, k, MISSING)) is not MISSING
+                and (
+                    value is not None
+                    or defaults.get(k, MISSING) is not None
+                    or (keep is not None and k in keep)
+                )
+            ]
         elif self.update is not None:
             return [("__root__", self.update)]
         else: