Fullstack Feature Developer

Guide feature development for Next.js/NestJS full-stack applications.

Extends: Generic Feature Developer - Read base skill for development workflow, decision frameworks, data flow patterns, and error handling.

Full-Stack Data Flow

User Action → Event Handler → API Call → NestJS Controller
                                              ↓
UI Update ← Response ← Service ← Prisma ← Database

Request/Response Cycle

// Frontend: Call API
const response = await fetch('/api/users', {
  method: 'POST',
  body: JSON.stringify(userData),
});

// Backend: Handle request
@Post()
@UseGuards(JwtAuthGuard)
async createUser(@Body() dto: CreateUserDto) {
  return this.userService.create(dto);
}

Next.js App Router Patterns

File Conventions

| File | Purpose | | ------------- | -------------------------------------- | | page.tsx | Route UI (server component by default) | | layout.tsx | Shared UI wrapper | | loading.tsx | Suspense loading UI | | error.tsx | Error boundary | | route.ts | API endpoint |

Server vs Client Components

// Server Component (default) - can fetch data
export default async function Page() {
  const data = await getData(); // Direct DB/API call
  return <div>{data.title}</div>;
}

// Client Component - needs 'use client'
'use client';
export default function Interactive() {
  const [state, setState] = useState();
  return <button onClick={() => setState(...)}>Click</button>;
}

NestJS Module Pattern

Module → Controller → Service → Prisma

Adding a Feature Module

// 1. Module definition
@Module({
  controllers: [UsersController],
  providers: [UsersService],
  exports: [UsersService],
})
export class UsersModule {}

// 2. Controller with guards
@Controller("users")
@UseGuards(JwtAuthGuard)
export class UsersController {
  @Post()
  create(@Body() dto: CreateUserDto) {
    return this.usersService.create(dto);
  }
}

// 3. Service with Prisma
@Injectable()
export class UsersService {
  constructor(private prisma: PrismaService) {}

  create(dto: CreateUserDto) {
    return this.prisma.user.create({ data: dto });
  }
}

Prisma Workflow

Schema Changes

# 1. Edit schema.prisma
# 2. Create migration
npx prisma migrate dev --name add_user_role

# 3. Regenerate client
npx prisma generate

# 4. Update services to use new fields

Type-Safe Queries

// ✓ Type-safe with generated types
const user = await this.prisma.user.findUnique({
  where: { id },
  include: { posts: true },
});

// ✗ Avoid raw SQL
await this.prisma.$queryRaw`SELECT * FROM users`; // No type safety

Authentication Flow

Login Request → Validate Credentials → Generate JWT → Set Cookie
      ↓
Protected Route → JwtAuthGuard → Extract User → Inject to Controller

Auth Integration Points

// Frontend: Include credentials
fetch('/api/protected', { credentials: 'include' });

// Backend: Guard + decorator
@UseGuards(JwtAuthGuard)
@Get('profile')
getProfile(@CurrentUser() user: User) {
  return user;
}

Feature Checklist (Fullstack)

Before Starting

[ ] Plan data model (Prisma schema)
[ ] Define API contract (DTOs)
[ ] Identify auth requirements

During Development

[ ] Create/update Prisma schema
[ ] Run migrations
[ ] Implement NestJS module (controller + service)
[ ] Create frontend components
[ ] Add loading/error states

Before Completion

[ ] Add DTO validation decorators
[ ] Write backend unit tests
[ ] Write E2E tests for API
[ ] Verify TypeScript types match

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