Access database connection defined in custom lifespan event when using `langgraph dev`

Product Help
1

LangGraph newbie here.

I am following the doc here: https://docs.langchain.com/langgraph-platform/custom-lifespan

How do i access for example app.state.db_session when using with langgraph dev (i.e. local server) if I need to use the db_session within a graph node?

2

In langgraph dev, you can’t access app.state.db_session directly from node config since LangGraph nodes run in isolation from the FastAPI app instance. You need to either:

Option 1: Inject into graph input

# Pass db_session when invoking the graph
graph.invoke({"messages": [...], "db_session": app.state.db_session})

def my_node(state, config):
    db_session = state["db_session"]
    return state

Option 2: Use a service locator/global utility

# Create a global service
class DatabaseService:
    db_session = None

# Set in lifespan, access in nodes
def my_node(state, config):
    db_session = DatabaseService.db_session
    return state

Lifespan objects must be explicitly passed or stored globally since nodes can’t access the FastAPI app state directly.