861b28b965
New skills (14): - nestjs-best-practices: 40 priority-ranked rules (kadajett) - fastapi: Pydantic v2, async SQLAlchemy, JWT auth (jezweb) - architecture-patterns: Clean Architecture, Hexagonal, DDD (wshobson) - python-performance-optimization: Profiling and optimization (wshobson) - ai-sdk: Vercel AI SDK streaming and agent patterns (vercel) - create-agent: Modular agent architecture with OpenRouter (openrouterteam) - proactive-agent: WAL Protocol, compaction recovery, self-improvement (halthelobster) - brand-guidelines: Brand identity enforcement (anthropics) - ui-animation: Motion design with accessibility (mblode) - marketing-ideas: 139 ideas across 14 categories (coreyhaines31) - pricing-strategy: SaaS pricing and tier design (coreyhaines31) - programmatic-seo: SEO at scale with playbooks (coreyhaines31) - competitor-alternatives: Comparison page architecture (coreyhaines31) - referral-program: Referral and affiliate programs (coreyhaines31) README reorganized by domain: Code Quality, Frontend, Backend, Auth, AI/Agent Building, Marketing, Design, Meta. Mosaic Stack is not limited to coding — the Orchestrator serves coding, business, design, marketing, writing, logistics, and analysis. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
107 lines
2.9 KiB
Markdown
107 lines
2.9 KiB
Markdown
---
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title: Single Responsibility for Services
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impact: CRITICAL
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impactDescription: "40%+ improvement in testability"
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tags: architecture, services, single-responsibility
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---
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## Single Responsibility for Services
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Each service should have a single, well-defined responsibility. Avoid "god services" that handle multiple unrelated concerns. If a service name includes "And" or handles more than one domain concept, it likely violates single responsibility. This reduces complexity and improves testability by 40%+.
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**Incorrect (god service anti-pattern):**
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```typescript
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// God service anti-pattern
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@Injectable()
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export class UserAndOrderService {
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constructor(
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private userRepo: UserRepository,
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private orderRepo: OrderRepository,
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private mailer: MailService,
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private payment: PaymentService,
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) {}
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async createUser(dto: CreateUserDto) {
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const user = await this.userRepo.save(dto);
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await this.mailer.sendWelcome(user);
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return user;
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}
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async createOrder(userId: string, dto: CreateOrderDto) {
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const order = await this.orderRepo.save({ userId, ...dto });
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await this.payment.charge(order);
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await this.mailer.sendOrderConfirmation(order);
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return order;
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}
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async calculateOrderStats(userId: string) {
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// Stats logic mixed in
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}
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async validatePayment(orderId: string) {
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// Payment logic mixed in
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}
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}
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```
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**Correct (focused services with single responsibility):**
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```typescript
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// Focused services with single responsibility
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@Injectable()
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export class UsersService {
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constructor(private userRepo: UserRepository) {}
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async create(dto: CreateUserDto): Promise<User> {
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return this.userRepo.save(dto);
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}
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async findById(id: string): Promise<User> {
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return this.userRepo.findOneOrFail({ where: { id } });
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}
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}
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@Injectable()
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export class OrdersService {
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constructor(private orderRepo: OrderRepository) {}
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async create(userId: string, dto: CreateOrderDto): Promise<Order> {
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return this.orderRepo.save({ userId, ...dto });
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}
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async findByUser(userId: string): Promise<Order[]> {
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return this.orderRepo.find({ where: { userId } });
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}
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}
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@Injectable()
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export class OrderStatsService {
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constructor(private orderRepo: OrderRepository) {}
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async calculateForUser(userId: string): Promise<OrderStats> {
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// Focused stats calculation
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}
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}
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// Orchestration in controller or dedicated orchestrator
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@Controller('orders')
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export class OrdersController {
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constructor(
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private orders: OrdersService,
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private payment: PaymentService,
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private notifications: NotificationService,
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) {}
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@Post()
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async create(@CurrentUser() user: User, @Body() dto: CreateOrderDto) {
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const order = await this.orders.create(user.id, dto);
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await this.payment.charge(order);
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await this.notifications.sendOrderConfirmation(order);
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return order;
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}
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}
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```
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Reference: [NestJS Providers](https://docs.nestjs.com/providers)
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