Dependency injection (Depends) yaya zai aiki?

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Accepted Answer

FastAPI's **dependency injection** system yana ba ku damar bayyana masu amfani abubuwa (ayyuka/azuzuwan) da FastAPI ke kira da **shigar** su cikin ayyukan hanya ku ta hanyar `Depends()`. Ana amfani da shi don ma'amala masu karfi kamar jeri-jerin bayanai, shaida, da ma'auni gama-gari — wajen ajiye code DRY da a iya gwaji.

## Abubuwa mai karfi na asali

```python
from fastapi import Depends

# a dependency is just a callable that returns something
def pagination(skip: int = 0, limit: int = 10):
    return {"skip": skip, "limit": limit}

@app.get("/items")
def list_items(params: dict = Depends(pagination)):   # FastAPI calls pagination() and injects the result
    return params
# the skip/limit query params are now handled by the reusable dependency
```

Bayyana `params = Depends(pagination)` yana gaya wa FastAPI a kira `pagination` (warware *saboda*ni parameter daga gaggawa ma) kuma watsar da sakamakon zuwa cikin aikin ku. Abu mai karfi ne da aka iya amfani da shi a wayaye masu karfi.

## Abubuwa masu karfi tare da tsari (yield) — misali jeri-jerin bayanai

```python
def get_db():
    db = SessionLocal()
    try:
        yield db                  # provide the session to the endpoint
    finally:
        db.close()                # cleanup runs AFTER the response — guaranteed

@app.get("/users")
def list_users(db = Depends(get_db)):
    return db.query(User).all()    # uses the injected, auto-closed session
```

`yield` dependency ya ba abu da kuma bugge tsari bayan bugi — tsarin sa'a don jeri-jerin bayanai (bude kafin, rufe bayan, ta atomatik).

## Abubuwa masu karfi na iya dogara a abubuwa masu karfi

```python
def get_current_user(token: str = Depends(get_token)):   # depends on another dependency
    return decode(token)

@app.get("/me")
def me(user: User = Depends(get_current_user)):           # auth via injection
    return user
```

Abubuwa masu karfi sun samar da itace — FastAPI yana warware gajeriyar. Wannan yadda aka yadu shaida akan jiya (abu mai karfi `get_current_user`).

## Azuzuwan karfi da amfani

```python
@app.get("/items", dependencies=[Depends(verify_api_key)])   # run a dependency without using its return
def items(): ...                                              # e.g. enforce auth as a side effect
```

## Me yasa ya matuhi

Dependency injection ina isa daga abubuwan da FastAPI ya karfe — shihinya yadda kuka iya bayyana da amfani da ma'amala jiya a wayaye marasa karfi (jeri-jerin bayanai, shaida, bugarni masu karfi, gwaje karya) ba tare da maimaitawa ba.
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