[Solved] Why does this FastAPI startup event handler fail?from fastapi import FastAPI app = FastAPI() @app.on_event("startup") def startup(): import asyncio asyncio.run(init_db()) | FastAPI

FastAPI - Middleware and Hooks

Why does this FastAPI startup event handler fail?

from fastapi import FastAPI
app = FastAPI()

@app.on_event("startup")
def startup():
    import asyncio
    asyncio.run(init_db())

AMissing await keyword before init_db()

BCalling asyncio.run inside event handler causes event loop error

Cinit_db() must be synchronous

DEvent handler must be named on_startup

Step-by-Step Solution

Solution:

Step 1: Understand asyncio.run usage
Calling asyncio.run() inside an already running event loop (FastAPI's) causes an error.
Step 2: Correct approach
Define the startup handler as async and await init_db() directly.
Final Answer:
Calling asyncio.run inside event handler causes event loop error -> Option B
Quick Check:
Don't call asyncio.run inside async event handlers [OK]

Quick Trick: Use async def and await, not asyncio.run inside handlers [OK]

Common Mistakes:

MISTAKES

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Why does this FastAPI startup event handler fail?