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fix(sessions): prevent PydanticSerializationError when session state contains non-serializable objects#4748

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fix(sessions): prevent PydanticSerializationError when session state contains non-serializable objects #4748

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fix(sessions): prevent PydanticSerializationError when state contains…
Raman369AI Mar 7, 2026
f2e73e9
fix(events): fix mypy errors in EventActions field serializers
Raman369AI Mar 18, 2026
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37 changes: 35 additions & 2 deletions src/google/adk/events/event_actions.py
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Original file line numberDiff line numberDiff line change
Expand Up@@ -14,21 +14,42 @@

from __future__ import annotations

import json
from typing import Any
from typing import cast
from typing import Optional

from google.genai.types import Content
from pydantic import alias_generators
from pydantic import BaseModel
from pydantic import ConfigDict
from pydantic import Field
from pydantic import field_serializer

from ..auth.auth_tool import AuthConfig
from ..tools.tool_confirmation import ToolConfirmation
from .ui_widget import UiWidget


class EventCompaction(BaseModel):
def _make_json_serializable(obj: Any) -> Any:
"""Recursively converts an object to a JSON-serializable form.

Non-serializable leaf values (e.g. Python callables stored in session state)
are replaced with a descriptive string so the overall structure can still be
persisted without crashing.
"""
if isinstance(obj, dict):
return {k: _make_json_serializable(v) for k, v in obj.items()}
if isinstance(obj, (list, tuple)):
return [_make_json_serializable(v) for v in obj]
try:
json.dumps(obj)
return obj
except (TypeError, ValueError):
return f'<not serializable: {type(obj).__name__}>'
Comment on lines +41 to +49

@gemini-code-assistgemini-code-assistBotMar 7, 2026

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medium

The current implementation of _make_json_serializable doesn't handle Pydantic BaseModel instances, which are not directly serializable by the standard json library. If a Pydantic model is present in the state, it will be incorrectly marked as non-serializable (<not serializable: ...>), leading to data that could have been persisted being lost.

To make this more robust, you should add a specific check for BaseModel instances and serialize them using obj.model_dump() before proceeding with the recursive serialization. This will ensure that Pydantic models within the state are correctly persisted.

Suggested change
ifisinstance(obj, dict):
return {k: _make_json_serializable(v) fork, vinobj.items()}
ifisinstance(obj, (list, tuple)):
return [_make_json_serializable(v) forvinobj]
try:
json.dumps(obj)
returnobj
except (TypeError, ValueError):
returnf'<not serializable: {type(obj).__name__}>'
ifisinstance(obj, BaseModel):
return_make_json_serializable(obj.model_dump())
ifisinstance(obj, dict):
return {k: _make_json_serializable(v) fork, vinobj.items()}
ifisinstance(obj, (list, tuple)):
return [_make_json_serializable(v) forvinobj]
try:
json.dumps(obj)
returnobj
except (TypeError, ValueError):
returnf'<not serializable: {type(obj).__name__}>'



class EventCompaction(BaseModel): # type: ignore[misc]
"""The compaction of the events."""

model_config = ConfigDict(
Expand All@@ -48,7 +69,7 @@ class EventCompaction(BaseModel):
"""The compacted content of the events."""


class EventActions(BaseModel):
class EventActions(BaseModel): # type: ignore[misc]
"""Represents the actions attached to an event."""

model_config = ConfigDict(
Expand All@@ -67,6 +88,10 @@ class EventActions(BaseModel):
state_delta: dict[str, object] = Field(default_factory=dict)
"""Indicates that the event is updating the state with the given delta."""

@field_serializer('state_delta', mode='plain') # type: ignore[misc, untyped-decorator]
def _serialize_state_delta(self, value: dict[str, object]) -> dict[str, Any]:
return cast(dict[str, Any], _make_json_serializable(value))

artifact_delta: dict[str, int] = Field(default_factory=dict)
"""Indicates that the event is updating an artifact. key is the filename,
value is the version."""
Expand DownExpand Up@@ -107,6 +132,14 @@ class EventActions(BaseModel):
"""The agent state at the current event, used for checkpoint and resume. This
should only be set by ADK workflow."""

@field_serializer('agent_state', mode='plain') # type: ignore[misc, untyped-decorator]
def _serialize_agent_state(
self, value: Optional[dict[str, Any]]
) -> Optional[dict[str, Any]]:
if value is None:
return None
return cast(dict[str, Any], _make_json_serializable(value))

rewind_before_invocation_id: Optional[str] = None
"""The invocation id to rewind to. This is only set for rewind event."""

Expand Down