Zaidi ya Depends ya msingi, dependency injection ya FastAPI inasaidia patterns za hali ya juu: sub-dependencies, dependencies zenye parameters (zinazotegemea class au kupitia factories), scoped resources (yield), , na kwa kupima (testing) — jambo linaloifanya kuwa zana inayobadilika kwa kupanga programu halisi.
def get_token(authorization: str = Header()):
return parse(authorization)
def get_current_user(token: str = Depends(get_token)): # depends on another dependency
return decode(token)
def get_admin(user: User = Depends(get_current_user)): # depends on that, in turn
if not user.is_admin: raise HTTPException(403)
return user
# FastAPI resolves the whole chain, caching shared dependencies within a request
Dependencies zinaweza kutegemea dependencies nyingine, zikiunda mti ambao FastAPI huutatua kiotomatiki (na huweka cache zile zinazoshirikiwa kwa kila request, kwa hivyo get_token huendeshwa mara moja hata ikitumiwa na dependencies kadhaa).
class RateLimiter:
def __init__(self, calls: int): # configure the dependency
self.calls = calls
def __call__(self, request: Request): # callable → acts as a dependency
check_rate_limit(request, self.calls)
@app.get("/items", dependencies=[Depends(RateLimiter(calls=100))]) # configured per route
def items(): ...
Class yenye __call__ ni dependency inayoweza kusanidiwa — unaiweka parameters wakati wa matumizi (mfano, rate limits tofauti kwa kila route).
@app.get("/admin", dependencies=[Depends(verify_admin)]) # run for the effect (auth check)
def admin(): ... # don't need its return value
app = FastAPI(dependencies=[Depends(verify_api_key)]) # applies to EVERY route
router = APIRouter(dependencies=[Depends(get_current_user)]) # to all routes in a router
Weka dependencies kwa programu nzima au kwa kila router kwa mahitaji ya cross-cutting (auth, rate limiting).
app.dependency_overrides[get_db] = get_test_db # swap any dependency in tests
Dependency injection ya FastAPI ni mojawapo ya vipengele vyake vyenye nguvu zaidi, na patterns hizi za hali ya juu ndizo zinazokuwezesha kupanga programu halisi, changamano kwa weledi.
Kuzielewa ni maarifa muhimu ya kiwango cha senior: sub-dependencies hujenga tabaka zinazoweza kutumika tena (token → user → admin) zenye utatuzi wa kiotomatiki na caching kwa kila request (zikiepuka kazi za kurudia); parameterized/class-based dependencies huunda vipengele vinavyoweza kusanidiwa na kutumika tena (rate limiters, ukaguzi wa ruhusa wenye mipangilio tofauti kwa kila route); dependencies kama side-effects hutekeleza mahitaji (auth) kwa usafi bila kujaza function signatures; na global/router-level dependencies huweka masuala ya cross-cutting (authentication, rate limiting) kwa makundi yote ya routes mahali pamoja.
Kwa umuhimu, dependency overrides hufanya hata grafu changamano za dependency kuwa rahisi kabisa kupima.
Kubobea patterns hizi — kuunganisha dependencies, kuziweka parameters, kuzitenga kimataifa au kwa kila router, na kuzibadilisha (override) katika tests — ndiko kunakowezesha usanifu safi, DRY, unaoweza kupimwa katika programu za FastAPI zisizo za kawaida, kikitofautisha wasanidi wanaoweza kutumia mfumo wa DI kikamilifu na wale wanaotumia Depends ya msingi tu.
Ni mada muhimu kwa kujenga programu za FastAPI zilizopangwa vizuri, zinazoweza kudumishwa, na za kiwango kikubwa.