NestJS API Backend Skill

Overview

This skill covers the NestJS GraphQL API backend that serves both web and native clients in the Game Critique project.

Technology Stack

• Framework: NestJS 10.x with TypeScript 5.3.3
• API: GraphQL with Apollo Server 4.x (@nestjs/graphql)
• Database: PostgreSQL with Prisma 5.6.x ORM
• Queue System: Bull with Redis for background jobs
• Authentication: JWT with Auth0 OAuth (passport-jwt, jwks-rsa)
• Compiler: SWC for fast builds
• Error Tracking: Sentry integration
• Web Scraping: Puppeteer for data extraction
• Image Storage: Cloudinary
• Validation: Zod schemas

Architecture Patterns

CQRS Pattern

The API uses Command Query Responsibility Segregation:

• Commands: Write operations that change state
• Queries: Read operations that return data
• Handlers: Process commands and queries

// Command example
export class UpdateGameDataCommand {
  constructor(public readonly hltbId: number) {}
}

// Command handler
@CommandHandler(UpdateGameDataCommand)
export class UpdateGameDataHandler {
  async execute(command: UpdateGameDataCommand) {
    // Implementation
  }
}

// Query example
export class GetGamesQuery {
  constructor(
    public readonly search: string,
    public readonly take: number,
    public readonly skip: number
  ) {}
}

Module Structure

Each feature follows this structure:

modules/
  <feature>/
    commands/              # CQRS commands
      <command_name>/
        <command_name>.command.ts
        <command_name>.handler.ts
    queries/               # CQRS queries
      <query_name>/
        <query_name>.query.ts
        <query_name>.handler.ts
    <feature>.module.ts    # NestJS module
    <feature>.service.ts   # Business logic
    <feature>.resolver.ts  # GraphQL resolver
    <feature>.repository.ts # Data access layer
    <feature>.dto.ts       # DTOs and GraphQL types
    <feature>.consumer.ts  # Bull queue consumer (if needed)

Repository Pattern

Data access is abstracted through repositories:

@Injectable()
export class GamesRepository {
  constructor(private readonly prisma: PrismaService) {}

  async getGameById(hltbId: number) {
    return this.prisma.game.findUnique({
      where: { hltbId },
      include: {
        cover: true,
        platformForGame: { include: { platform: true } },
        genres: { include: { genre: true } },
        release: true,
        completionTime: true,
      },
    });
  }
}

GraphQL Patterns

Code-First Approach

Schema is generated from TypeScript decorators:

// DTOs with GraphQL decorators
@ObjectType()
export class GameWithAllDataDTO {
  @Field(() => Int)
  hltbId: number;

  @Field()
  title: string;

  @Field(() => [PlatformDTO])
  platforms: PlatformDTO[];
}

@ArgsType()
export class GetPaginatedGamesArgs {
  @Field({ nullable: true })
  search?: string;

  @Field(() => Int, { defaultValue: 10 })
  take: number;

  @Field(() => Int, { defaultValue: 0 })
  skip: number;
}

// Resolver
@Resolver()
export class GamesResolver {
  constructor(private readonly gamesService: GamesService) {}

  @Query(() => GameWithAllDataDTO, { name: 'game' })
  async getGameById(@Args('hltbId') hltbId: number) {
    return this.gamesService.getGameById(hltbId);
  }

  @UseGuards(JwtAuthGuard, AdminUserGuard)
  @Mutation(() => UpdateGameDataDTO, { name: 'updateGameData' })
  async updateGameData(@Args('hltbId') hltbId: number) {
    return this.gamesService.updateGameData(hltbId);
  }
}

Guards for Authorization

// JWT Authentication
@UseGuards(JwtAuthGuard)
@Query(() => UserProfile)
async getProfile(@CurrentUser() user: User) {
  return this.profilesService.getProfile(user.oauthId);
}

// Admin-only operations
@UseGuards(JwtAuthGuard, AdminUserGuard)
@Mutation(() => Boolean)
async deleteUser(@Args('userId') userId: number) {
  return this.usersService.deleteUser(userId);
}

Database with Prisma

Schema Definition

model User {
  id                Int                @id @default(autoincrement())
  oauthId           String             @unique @map("oauth_id")
  createdAt         DateTime           @default(now()) @map("created_at")
  updatedAt         DateTime           @updatedAt @map("updated_at")
  profile           Profile?
  GamesStatus       GamesStatus[]
  role              UserRole?

  @@map("users")
}

Migration Workflow

# 1. Update schema.prisma
# 2. Create migration
yarn prisma-migrate-dev <migration-name>

# 3. Generate client
yarn prisma-generate

# 4. Update repositories and DTOs

Background Jobs with Bull

Queue Setup

// In module
BullModule.registerQueue({
  name: 'games',
}),

// In service
constructor(
  @InjectQueue('games') private gamesQueue: Queue,
) {}

async addGamesToDatabase(games: GameData[]) {
  return this.gamesQueue.add('createGame', games);
}

// Consumer
@Processor('games')
export class GamesConsumer {
  @Process('createGame')
  async handleCreateGame(job: Job<GameData[]>) {
    // Process job
  }
}

Error Handling

Always use proper HTTP exceptions:

import { HttpException, HttpStatus } from '@nestjs/common';

if (!game) {
  throw new HttpException(
    {
      status: HttpStatus.NOT_FOUND,
      message: 'Nie znaleziono gry o podanym ID',
    },
    HttpStatus.NOT_FOUND,
  );
}

Key Modules

Existing Modules

• auth: JWT authentication with Auth0
• games: Game CRUD operations, IGDB integration
• search: Game search functionality
• profiles: User profile management
• collections: User game collections
• games_status: Track user's game progress
• friends: Friend system with requests
• images: Cloudinary image uploads
• roles: User role management (Admin/User)
• platforms: Gaming platform data
• user_stats: User statistics and analytics
• howlongtobeat_migration: Data migration from HowLongToBeat
• howlongtobeat_parser: Web scraping with Puppeteer

Development Commands

# Development
yarn dev                    # Watch mode
yarn start:debug           # Debug mode

# Building
yarn build                 # Production build with SWC

# Database
yarn start:db              # Start PostgreSQL + Redis with Docker
yarn prisma-generate       # Generate Prisma client
yarn prisma-migrate-dev    # Create new migration
yarn prisma-seed           # Seed database

# Testing
yarn test:implement        # Run unit tests
yarn test:e2e             # Run e2e tests
yarn test:cov             # Coverage report

# Code Quality
yarn lint                  # ESLint
yarn format               # Prettier

Best Practices

1. Always use CQRS for complex operations
2. Use repositories for all data access
3. Implement proper guards for protected routes
4. Use Zod for runtime validation when needed
5. Handle errors with HttpException
6. Add logging with AppLoggerMiddleware context
7. Use Bull queues for long-running operations
8. Keep resolvers thin - delegate to services
9. Use transactions for multi-step database operations
10. Add tests for critical business logic

Adding a New Feature

Step-by-Step Guide

# 1. Generate module
nest g module modules/<feature>

# 2. Generate service and resolver
nest g service modules/<feature>
nest g resolver modules/<feature>

# 3. Create repository
# Create <feature>.repository.ts

# 4. Create DTOs with GraphQL decorators
# Create <feature>.dto.ts

# 5. Implement CQRS if needed
mkdir -p src/modules/<feature>/commands
mkdir -p src/modules/<feature>/queries

# 6. Add guards for protected operations

# 7. Register in app.module.ts

# 8. Schema auto-generates on startup

Testing Example

describe('GamesService', () => {
  let service: GamesService;
  let repository: GamesRepository;

  beforeEach(async () => {
    const module: TestingModule = await Test.createTestingModule({
      providers: [
        GamesService,
        {
          provide: GamesRepository,
          useValue: {
            getGameById: jest.fn(),
          },
        },
      ],
    }).compile();

    service = module.get<GamesService>(GamesService);
    repository = module.get<GamesRepository>(GamesRepository);
  });

  it('should return a game by id', async () => {
    const mockGame = { hltbId: 1, title: 'Test Game' };
    jest.spyOn(repository, 'getGameById').mockResolvedValue(mockGame);

    const result = await service.getGameById(1);
    expect(result).toEqual(mockGame);
  });
});

Environment Variables

Required environment variables:

# Database
DATABASE_URL=postgresql://user:password@localhost:5432/game_critique

# Redis
REDIS_HOST=localhost
REDIS_PORT=6379

# Auth0
AUTH0_DOMAIN=your-domain.auth0.com
AUTH0_AUDIENCE=your-audience

# External APIs
IGDB_CLIENT_ID=your-client-id
IGDB_CLIENT_SECRET=your-client-secret

# Cloudinary
CLOUDINARY_CLOUD_NAME=your-cloud
CLOUDINARY_API_KEY=your-key
CLOUDINARY_API_SECRET=your-secret

# Sentry
SENTRY_DSN=your-dsn

# App
NODE_ENV=development
PORT=3000

Common Patterns

Service with CQRS

@Injectable()
export class GamesService {
  constructor(
    private readonly queryBus: QueryBus,
    private readonly commandBus: CommandBus,
  ) {}

  async getPaginatedGames(args: GetPaginatedGamesArgs) {
    return this.queryBus.execute(
      new GetGamesQuery(args.search, args.take, args.skip)
    );
  }

  async updateGameData(hltbId: number) {
    return this.commandBus.execute(
      new UpdateGameDataCommand(hltbId)
    );
  }
}

Scheduled Tasks

import { Cron, CronExpression } from '@nestjs/schedule';

@Injectable()
export class TasksService {
  @Cron(CronExpression.EVERY_DAY_AT_MIDNIGHT)
  async handleDailyTask() {
    // Execute task
  }
}