Lit Element Domain Driven Design DDD

💡 แนะนำ: ผมเขียนไว้ละเอียดกว่านี้ที่

# ═══════════════════════════════════════
# Lit Element Domain Driven Design DDD — Basic Implementation
# Language: JavaScript + Gin
# ═══════════════════════════════════════

# 2. Initialize project
npm init -y # Node.js

# 3. Install dependencies
npm install -D typescript @types/node jest

// ═══════════════════════════════════════
// Lit Element Domain Driven Design DDD — Production Implementation
// ═══════════════════════════════════════

import { logger, cors, rateLimit, helmet } from './middleware';
import { db } from './database';
import { cache } from './cache';

// Initialize application
const app = createApp({
 version: '2.0.0'
 env: process.env.NODE_ENV || 'development'
});

// Database connection
const database = db.connect({
 host: process.env.DB_HOST || 'localhost'
 port: parseInt(process.env.DB_PORT || '5432')
 pool: { min: 5, max: 25 }
});

// Cache connection
const redisCache = cache.connect({
 host: process.env.REDIS_HOST || 'localhost'
 port: 6379
 ttl: 3600, // 1 hour default
});

// Middleware stack
app.use(helmet()); // Security headers
app.use(cors({ origin: process.env.ALLOWED_ORIGINS }));
app.use(logger({ level: 'info', format: 'json' }));
app.use(rateLimit({ max: 100, window: '1m' }));

// Health check endpoint
app.get('/health', async (req, res) => {
 const dbHealth = await database.ping();
 const cacheHealth = await redisCache.ping();
 res.json({
 status: dbHealth && cacheHealth ? 'healthy' : 'degraded'
 uptime: process.uptime()
 timestamp: new Date().toISOString()
 checks: {
 database: dbHealth ? 'ok' : 'error'
 cache: cacheHealth ? 'ok' : 'error'
 }
 });
});

// API Routes
const router = createRouter();

router.get('/api/v1/items', async (req, res) => {
 const { page = 1, limit = 20, search } = req.query;
 const cacheKey = `items:::`;

 // Try cache first
 const cached = await redisCache.get(cacheKey);
 if (cached) return res.json(JSON.parse(cached));

 // Query database
 const items = await database.query(
 'SELECT * FROM items WHERE ($1::text IS NULL OR name ILIKE $1) ORDER BY created_at DESC LIMIT $2 OFFSET $3'
 [search ? `%%` : null, limit, (page - 1) * limit]
 );

 const result = { data: items.rows, page, limit, total: items.rowCount };
 await redisCache.set(cacheKey, JSON.stringify(result), 300);
 res.json(result);
});

app.use(router);

// Graceful shutdown
process.on('SIGTERM', async () => {
 console.log('Shutting down gracefully...');
 await database.close();
 await redisCache.close();
 process.exit(0);
});

// Start server
const PORT = parseInt(process.env.PORT || '3000');
app.listen(PORT, () => {
});

Design Patterns ที่ใช้บ่อยกับ Lit Element Domain Driven Design DDD

Pattern	ใช้เมื่อ	ตัวอย่างจริง	ภาษาที่เหมาะ
Singleton	ต้องการ instance เดียวทั้ง app	Database connection pool, Logger, Config	ทุกภาษา
Factory	สร้าง object หลายประเภทจาก interface เดียว	Payment gateway (Stripe/PayPal/Omise), Notification (Email/SMS/Push)	Java, C#, TypeScript
Observer	Event-driven architecture	WebSocket real-time updates, Pub/Sub messaging	JavaScript, Python
Strategy	เปลี่ยน algorithm ได้ตอน runtime	Sorting algorithms, Authentication methods, Pricing strategies	ทุกภาษา
Repository	แยก data access logic ออกจาก business logic	Database queries, API calls to external services	Java, C#, TypeScript
Middleware/Pipeline	ประมวลผล request ผ่านหลาย step	Express middleware, Django middleware, ASP.NET pipeline	JavaScript, Python, C#
Builder	สร้าง complex object ทีละ step	Query builder, Form builder, Report generator	Java, TypeScript

SOLID Principles — หลักการเขียนโค้ดที่ดี

• Single Responsibility — แต่ละ class/function ทำหน้าที่เดียวถ้า function ยาวเกิน 20 บรรทัดควรแยกออก
• Open/Closed — เปิดสำหรับ extension ปิดสำหรับ modification ใช้ interface/abstract class
• Liskov Substitution — subclass ต้องแทนที่ parent ได้โดยไม่ทำให้ระบบพัง
• Interface Segregation — แยก interface ให้เล็กและเฉพาะเจาะจงอย่าสร้าง "God Interface"
• Dependency Inversion — depend on abstractions ไม่ใช่ implementations ใช้ Dependency Injection

Clean Code Practices

• Meaningful Names — ตั้งชื่อตัวแปร/function ให้สื่อความหมาย getUserById(id) ดีกว่า get(x)
• Small Functions — function ควรทำสิ่งเดียวยาวไม่เกิน 20 บรรทัด
• DRY (Don't Repeat Yourself) — ถ้าเขียนโค้ดซ้ำ 3 ครั้งควร refactor เป็น function
• Error Handling — จัดการ error อย่างเหมาะสมไม่ swallow exceptions
• Comments — โค้ดที่ดีอธิบายตัวเองได้ใช้ comment เฉพาะเมื่อจำเป็น (why, not what)

Testing Strategy

// ═══════════════════════════════════════
// Unit Tests — Pytest
// ═══════════════════════════════════════

describe('Lit Element Domain Driven Design DDD Core Functions', () => {
 // Setup
 beforeEach(() => {
 jest.clearAllMocks();
 });

 it('should process data correctly', () => {
 const input = { name: 'test', value: 42 };
 const result = processData(input);
 expect(result).toBeDefined();
 expect(result.status).toBe('success');
 expect(result.processedValue).toBe(84);
 });

 it('should handle null input gracefully', () => {
 expect(() => processData(null)).toThrow('Input cannot be null');
 });

 it('should handle empty object', () => {
 const result = processData({});
 expect(result.status).toBe('error');
 expect(result.message).toContain('missing required fields');
 });

 it('should validate input types', () => {
 const input = { name: 123, value: 'not a number' };
 expect(() => processData(input)).toThrow('Invalid input types');
 });
});

// ═══════════════════════════════════════
// Integration Tests
// ═══════════════════════════════════════
describe('API Integration Tests', () => {
 it('GET /api/v1/items should return 200', async () => {
 const res = await request(app).get('/api/v1/items');
 expect(res.status).toBe(200);
 expect(res.body.data).toBeInstanceOf(Array);
 });

 it('POST /api/v1/items should create item', async () => {
 const res = await request(app)
 .post('/api/v1/items')
 .send({ name: 'Test Item', value: 100 })
 .set('Authorization', `Bearer `);
 expect(res.status).toBe(201);
 expect(res.body.id).toBeDefined();
 });

 it('should return 401 without auth', async () => {
 const res = await request(app).post('/api/v1/items').send({});
 expect(res.status).toBe(401);
 });
});

CI/CD Pipeline

# .github/workflows/ci.yml
# ═══════════════════════════════════════
name: CI/CD Pipeline
on:
 push:
 branches: [main, develop]
 pull_request:
 branches: [main]

jobs:
 test:
 runs-on: ubuntu-latest
 services:
 postgres:
 image: postgres:16
 env:
 POSTGRES_PASSWORD: test
 ports: ['5432:5432']
 redis:
 image: redis:7
 ports: ['6379:6379']
 steps:
 - uses: actions/checkout@v4
 - uses: actions/setup-node@v4
 with:
 node-version: '20'
 cache: 'npm'
 - run: npm ci
 - run: npm run lint
 - run: npm run type-check
 - run: npm test -- --coverage
 - uses: codecov/codecov-action@v4

 build:
 needs: test
 runs-on: ubuntu-latest
 steps:
 - uses: actions/checkout@v4
 - uses: docker/build-push-action@v5
 with:
 push: }
 tags: ghcr.io/}:latest

 deploy:
 needs: build
 if: github.ref == 'refs/heads/main'
 runs-on: ubuntu-latest
 steps:
 - run: echo "Deploying to production..."
 # Add your deployment steps here