How can I create a tool for langgaph's agent to save data in db?

I created an agent using Langgraph in Python, and I developed a tool for them to save a todo in a database. But that tool doesn't work and raises an error!

I use SQLAlchemy to connect to the DB.

This is my DB code:

from datetime import datetime from sqlalchemy import DateTime from sqlalchemy.ext.asyncio import create_async_engine, async_sessionmaker, AsyncSession from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column engine = create_async_engine( settings.DATABASE_URL, pool_size=20, max_overflow=40, pool_timeout=30, pool_pre_ping=True, ) AsyncSessionLocal = async_sessionmaker( engine, class_=AsyncSession, expire_on_commit=False, autoflush=False, autocommit=False, )

and this is my agent:

async def run_agent(thread_id:int, human_message:str) -> MessagesState: """ talk with your agent or execute agent Args: thread_id (int): thread id human_message (str): message of human Returns: MessagesState: return MessagesState """ config = {"configurable": {"thread_id": thread_id}} async with AsyncSqliteSaver.from_conn_string(settings.AI_MEMORY_DB) as checkpointer: agent = create_agent( model=chat_model, tools=TOOLS, system_prompt=settings.SYSTEM_PROMPT, checkpointer=checkpointer ) res = await agent.ainvoke({"messages": HumanMessage(human_message)}, config=config) return res

and this is my tools:

@tool async def create_todo(date:str, time:str, title:str) -> str: """ Use this tool IMMEDIATELY and WITHOUT EXCEPTION whenever the user wants to create a new todo, reminder, appointment, plan, or schedule anything for the future. This tool stores the user's schedule in a database so that it can be better recalled later and reports can be generated on the tasks. You MUST call this tool when you see phrases like: - Remind me to ... - Set a reminder for ... - Create a todo for ... - I have a meeting/appointment/plan on ... - Remember to call someone tomorrow - Schedule something - Don't let me forget to ... - Put in my calendar ... Even if the user speaks in Persian (Farsi) or gives the date in Persian calendar (Shamsi), you MUST convert it to Gregorian (YYYY-MM-DD) yourself and call this tool. Examples that MUST trigger this tool: - "Remind me to go to the doctor next Monday at 3 PM" - "Set a reminder for December 25, 2025 at 14:30 for team meeting" Args: date (str): Date in EXACT YYYY-MM-DD format (example: 2025-11-26, 2025-12-25) time (str): Time in 24-hour HH:MM format with leading zeros (example: 09:30, 17:00, 08:15) title (str): Full title or description of the task/reminder exactly as the user wants it saved Returns: str: Success or error message """ try: async with AsyncSessionLocal() as session: async with session.begin(): _datetime = f"{date} {time}" datetime_to_do_it = await sync_to_async(datetime.strptime)(_datetime, "%Y-%m-%d %H:%M") todo = Todo(title=title, datetime_to_do_it=datetime_to_do_it) session.add(todo) return "todo sucessfuly saved" except Exception as ex: return f"something wrong! {ex}" TOOLS = [ create_todo, ]

But when I want my agent to save my todo, that doesn't work and raises an error:

Exception terminating connection <AdaptedConnection <asyncpg.connection.Connection object at 0x7f1f5017dc70>> Traceback (most recent call last): File "/home/user/Documents/python_projects/Diana/venv/lib/python3.12/site-packages/sqlalchemy/pool/base.py", line 372, in _close_connection self._dialect.do_terminate(connection) File "/home/user/Documents/python_projects/Diana/venv/lib/python3.12/site-packages/sqlalchemy/dialects/postgresql/asyncpg.py", line 1127, in do_terminate dbapi_connection.terminate() File "/home/user/Documents/python_projects/Diana/venv/lib/python3.12/site-packages/sqlalchemy/connectors/asyncio.py", line 402, in terminate self.await_(asyncio.shield(self._terminate_graceful_close())) # type: ignore[attr-defined] # noqa: E501 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/home/user/Documents/python_projects/Diana/venv/lib/python3.12/site-packages/sqlalchemy/util/_concurrency_py3k.py", line 132, in await_only return current.parent.switch(awaitable) # type: ignore[no-any-return,attr-defined] # noqa: E501 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/home/user/Documents/python_projects/Diana/venv/lib/python3.12/site-packages/sqlalchemy/util/_concurrency_py3k.py", line 196, in greenlet_spawn value = await result ^^^^^^^^^^^^ File "/home/user/Documents/python_projects/Diana/venv/lib/python3.12/site-packages/sqlalchemy/dialects/postgresql/asyncpg.py", line 912, in _terminate_graceful_close await self._connection.close(timeout=2) File "/home/user/Documents/python_projects/Diana/venv/lib/python3.12/site-packages/asyncpg/connection.py", line 1504, in close await self._protocol.close(timeout) File "asyncpg/protocol/protocol.pyx", line 627, in close File "asyncpg/protocol/protocol.pyx", line 660, in asyncpg.protocol.protocol.BaseProtocol._request_cancel File "/home/user/Documents/python_projects/Diana/venv/lib/python3.12/site-packages/asyncpg/connection.py", line 1673, in _cancel_current_command self._cancellations.add(self._loop.create_task(self._cancel(waiter))) ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/usr/lib/python3.12/asyncio/base_events.py", line 456, in create_task self._check_closed() File "/usr/lib/python3.12/asyncio/base_events.py", line 541, in _check_closed raise RuntimeError('Event loop is closed') RuntimeError: Event loop is closed ^C^Csys:1: RuntimeWarning: coroutine 'Connection._cancel' was never awaited RuntimeWarning: Enable tracemalloc to get the object allocation traceback

I know this error raises when my agent wants to use it because I tested it in IPython.