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pythonintermediate

FastAPI Dependency Injection

Use FastAPI's dependency injection for database sessions, auth checks, and shared service logic.

python
from fastapi import FastAPI, Depends, HTTPException
from typing import Annotated

app = FastAPI()

# Simulated DB session
async def get_db():
    db = {"connected": True}  # Replace with real session
    try:
        yield db
    finally:
        pass  # Close session here

async def get_current_user(
    token: str = "",  # Normally from header
    db=Depends(get_db),
):
    if not token:
        raise HTTPException(status_code=401, detail="Not authenticated")
    return {"id": "user_1", "name": "Alice"}

DB = Annotated[dict, Depends(get_db)]
User = Annotated[dict, Depends(get_current_user)]

@app.get("/profile")
async def get_profile(user: User, db: DB):
    return {"user": user, "db_connected": db["connected"]}

Use Cases

  • Database session management
  • Authentication middleware
  • Service layer injection

Tags

#fastapi#dependency-injection#api#python

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