Menene tsarin halittar bukatun NestJS?

Question

Accepted Answer

**Tsarin halittar bukatun** shine lissafin daidai na sassan da bukatun ya wuce su a cikin NestJS — middleware, guards, interceptors, pipes, handler, sannan interceptors sake, da exception filters akan kuskure. Sanin daidai tsari aiki shi ne mahimmancin a fahimci *a lokacin* kowane yanki na ilimi zai gudna.

## The full order

```text
Incoming Request
   │
   ▼
1. MIDDLEWARE            (Express-style; raw req/res; runs first)
   │
   ▼
2. GUARDS                (authorization — return true to continue, false/throw to block)
   │
   ▼
3. INTERCEPTORS (pre)    (logic BEFORE the handler — start timing, etc.)
   │
   ▼
4. PIPES                 (validate/transform the handler's arguments — DTO validation)
   │
   ▼
5. ROUTE HANDLER         (your controller method runs)
   │
   ▼
6. INTERCEPTORS (post)   (logic AFTER the handler — transform the response)
   │
   ▼
Response

✗ If an exception is thrown ANYWHERE above →
7. EXCEPTION FILTERS     (catch it and format the error response)
```

## Why the order matters (practical consequences)

```text
• Guards run BEFORE pipes → authorization is checked before input validation
  (no point validating a body for an unauthorized request)
• Pipes run JUST BEFORE the handler → the handler always gets validated/transformed args
• Interceptors straddle the handler → they can measure its duration and transform output
• Filters catch errors from any stage → centralized, consistent error handling
```

## Within each category, scope ordering applies

```text
For each type (guards, interceptors, pipes), they run in this scope order:
  Global → Controller → Method (route)
So a global guard runs before a controller-level guard, before a route-level guard.
```

## A concrete example

```ts
@Controller("users")
@UseGuards(AuthGuard)                    // 2. checks authorization
@UseInterceptors(LoggingInterceptor)     // 3 (pre) + 6 (post)
export class UsersController {
  @Post()
  create(@Body() dto: CreateUserDto) {    // 4. ValidationPipe validates dto, 5. handler runs
    return this.usersService.create(dto);
  }
}
// Flow: middleware → AuthGuard → LoggingInterceptor(before) → ValidationPipe →
//       create() → LoggingInterceptor(after) → response (or → filter on error)
```

## Me ya sa haka muhimmi

Fahimtar tsarin halittar bukatun aiki shi ne tushen gina takarar NestJS da kyau — tana bayanin daidai *a lokacin* kowane yanki na ilimin waje ya gudna, wanda ke nauyi zuwa ganin niyyar da bugi.

Tsari yana da ainihi, tasiri na fada: **guards suna gudu kafin pipes**, don haka i'tibar a gari sannan kafin shiryawa shiryawa (bukatun ba gida ba a kin kafin shiryawa); **pipes suna gudu kafin handler**, ba da garantin handler a kula sauya argoma; **interceptors suna damre handler** (gudu kafin *da* bayan), wanda shine daidai ya ba su damar lokaci aiki da sauya amsa; da **exception filters suna karya kurakuran daga kowane mataki**, ba da damar tsakanin jiya.

Sanin wannan tsari — da kuma tsarin waje a cikin kowane rukunin (duniya → controller → hanya) — ya ba ku hanya sa ilimi a sassan gida, sani amfani, bugi yini don me abin gudu (ko ba ya yi gudu) lokacin da aka saba, da gini fasali a kyau.

Ya rera mulkin tsaftarwa duka na bukatun tsari-saran (middleware, guards, interceptors, pipes, filters) cikin lissafin tunani gida, wanda ke sa shi abin muhimmi, gwajin yau-da-kullun da yakake fahimce sosai ta hanyar yun NestJS bukatun.