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Kodelyth ECC
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backend-patterns

Backend architecture patterns, API design, database optimization, and server-side best practices for Node.js, Express, and Next.js API routes.

Invoke via:use backend-patterns
Origin:ECC

Backend Development Patterns

Backend architecture patterns and best practices for scalable server-side applications.

When to Activate

  • Designing REST or GraphQL API endpoints
  • Implementing repository, service, or controller layers
  • Optimizing database queries (N+1, indexing, connection pooling)
  • Adding caching (Redis, in-memory, HTTP cache headers)
  • Setting up background jobs or async processing
  • Structuring error handling and validation for APIs
  • Building middleware (auth, logging, rate limiting)

API Design Patterns

RESTful API Structure

// PASS: Resource-based URLs
GET    /api/markets                 # List resources
GET    /api/markets/:id             # Get single resource
POST   /api/markets                 # Create resource
PUT    /api/markets/:id             # Replace resource
PATCH  /api/markets/:id             # Update resource
DELETE /api/markets/:id             # Delete resource
// PASS: Query parameters for filtering, sorting, pagination
GET /api/markets?status=active&sort=volume&limit=20&offset=0

Repository Pattern

// Abstract data access logic
interface MarketRepository {
  findAll(filters?: MarketFilters): Promise<Market[]>
  findById(id: string): Promise<Market | null>
  create(data: CreateMarketDto): Promise<Market>
  update(id: string, data: UpdateMarketDto): Promise<Market>
  delete(id: string): Promise<void>
}
class SupabaseMarketRepository implements MarketRepository {
  async findAll(filters?: MarketFilters): Promise<Market[]> {
    let query = supabase.from('markets').select('*')
    if (filters?.status) {
      query = query.eq('status', filters.status)
    }
    if (filters?.limit) {
      query = query.limit(filters.limit)
    }
    const { data, error } = await query
    if (error) throw new Error(error.message)
    return data
  }
  // Other methods...
}

Service Layer Pattern

// Business logic separated from data access
class MarketService {
  constructor(private marketRepo: MarketRepository) {}
  async searchMarkets(query: string, limit: number = 10): Promise<Market[]> {
    // Business logic
    const embedding = await generateEmbedding(query)
    const results = await this.vectorSearch(embedding, limit)
    // Fetch full data
    const markets = await this.marketRepo.findByIds(results.map(r => r.id))
    // Sort by similarity
    return markets.sort((a, b) => {
      const scoreA = results.find(r => r.id === a.id)?.score || 0
      const scoreB = results.find(r => r.id === b.id)?.score || 0
      return scoreA - scoreB
    })
  }
  private async vectorSearch(embedding: number[], limit: number) {
    // Vector search implementation
  }
}

Middleware Pattern

// Request/response processing pipeline
export function withAuth(handler: NextApiHandler): NextApiHandler {
  return async (req, res) => {
    const token = req.headers.authorization?.replace('Bearer ', '')
    if (!token) {
      return res.status(401).json({ error: 'Unauthorized' })
    }
    try {
      const user = await verifyToken(token)
      req.user = user
      return handler(req, res)
    } catch (error) {
      return res.status(401).json({ error: 'Invalid token' })
    }
  }
}
// Usage
export default withAuth(async (req, res) => {
  // Handler has access to req.user
})

Database Patterns

Query Optimization

// PASS: GOOD: Select only needed columns
const { data } = await supabase
  .from('markets')
  .select('id, name, status, volume')
  .eq('status', 'active')
  .order('volume', { ascending: false })
  .limit(10)
// FAIL: BAD: Select everything
const { data } = await supabase
  .from('markets')
  .select('*')

N+1 Query Prevention

// FAIL: BAD: N+1 query problem
const markets = await getMarkets()
for (const market of markets) {
  market.creator = await getUser(market.creator_id)  // N queries
}
// PASS: GOOD: Batch fetch
const markets = await getMarkets()
const creatorIds = markets.map(m => m.creator_id)
const creators = await getUsers(creatorIds)  // 1 query
const creatorMap = new Map(creators.map(c => [c.id, c]))
markets.forEach(market => {
  market.creator = creatorMap.get(market.creator_id)
})

Transaction Pattern

async function createMarketWithPosition(
  marketData: CreateMarketDto,
  positionData: CreatePositionDto
) {
  // Use Supabase transaction
  const { data, error } = await supabase.rpc('create_market_with_position', {
    market_data: marketData,
    position_data: positionData
  })
  if (error) throw new Error('Transaction failed')
  return data
}
// SQL function in Supabase
CREATE OR REPLACE FUNCTION create_market_with_position(
  market_data jsonb,
  position_data jsonb
)
RETURNS jsonb
LANGUAGE plpgsql
AS $$
BEGIN
  -- Start transaction automatically
  INSERT INTO markets VALUES (market_data);
  INSERT INTO positions VALUES (position_data);
  RETURN jsonb_build_object('success', true);
EXCEPTION
  WHEN OTHERS THEN
    -- Rollback happens automatically
    RETURN jsonb_build_object('success', false, 'error', SQLERRM);
END;
$$;

Caching Strategies

Redis Caching Layer

class CachedMarketRepository implements MarketRepository {
  constructor(
    private baseRepo: MarketRepository,
    private redis: RedisClient
  ) {}
  async findById(id: string): Promise<Market | null> {
    // Check cache first
    const cached = await this.redis.get(market:${id})
    if (cached) {
      return JSON.parse(cached)
    }
    // Cache miss - fetch from database
    const market = await this.baseRepo.findById(id)
    if (market) {
      // Cache for 5 minutes
      await this.redis.setex(market:${id}, 300, JSON.stringify(market))
    }
    return market
  }
  async invalidateCache(id: string): Promise<void> {
    await this.redis.del(market:${id})
  }
}

Cache-Aside Pattern

async function getMarketWithCache(id: string): Promise<Market> {
  const cacheKey = market:${id}
  // Try cache
  const cached = await redis.get(cacheKey)
  if (cached) return JSON.parse(cached)
  // Cache miss - fetch from DB
  const market = await db.markets.findUnique({ where: { id } })
  if (!market) throw new Error('Market not found')
  // Update cache
  await redis.setex(cacheKey, 300, JSON.stringify(market))
  return market
}

Error Handling Patterns

Centralized Error Handler

class ApiError extends Error {
  constructor(
    public statusCode: number,
    public message: string,
    public isOperational = true
  ) {
    super(message)
    Object.setPrototypeOf(this, ApiError.prototype)
  }
}
export function errorHandler(error: unknown, req: Request): Response {
  if (error instanceof ApiError) {
    return NextResponse.json({
      success: false,
      error: error.message
    }, { status: error.statusCode })
  }
  if (error instanceof z.ZodError) {
    return NextResponse.json({
      success: false,
      error: 'Validation failed',
      details: error.errors
    }, { status: 400 })
  }
  // Log unexpected errors
  console.error('Unexpected error:', error)
  return NextResponse.json({
    success: false,
    error: 'Internal server error'
  }, { status: 500 })
}
// Usage
export async function GET(request: Request) {
  try {
    const data = await fetchData()
    return NextResponse.json({ success: true, data })
  } catch (error) {
    return errorHandler(error, request)
  }
}

Retry with Exponential Backoff

async function fetchWithRetry<T>(
  fn: () => Promise<T>,
  maxRetries = 3
): Promise<T> {
  let lastError: Error
  for (let i = 0; i < maxRetries; i++) {
    try {
      return await fn()
    } catch (error) {
      lastError = error as Error
      if (i < maxRetries - 1) {
        // Exponential backoff: 1s, 2s, 4s
        const delay = Math.pow(2, i) * 1000
        await new Promise(resolve => setTimeout(resolve, delay))
      }
    }
  }
  throw lastError!
}
// Usage
const data = await fetchWithRetry(() => fetchFromAPI())

Authentication & Authorization

JWT Token Validation

import jwt from 'jsonwebtoken'
interface JWTPayload {
  userId: string
  email: string
  role: 'admin' | 'user'
}
export function verifyToken(token: string): JWTPayload {
  try {
    const payload = jwt.verify(token, process.env.JWT_SECRET!) as JWTPayload
    return payload
  } catch (error) {
    throw new ApiError(401, 'Invalid token')
  }
}
export async function requireAuth(request: Request) {
  const token = request.headers.get('authorization')?.replace('Bearer ', '')
  if (!token) {
    throw new ApiError(401, 'Missing authorization token')
  }
  return verifyToken(token)
}
// Usage in API route
export async function GET(request: Request) {
  const user = await requireAuth(request)
  const data = await getDataForUser(user.userId)
  return NextResponse.json({ success: true, data })
}

Role-Based Access Control

type Permission = 'read' | 'write' | 'delete' | 'admin'
interface User {
  id: string
  role: 'admin' | 'moderator' | 'user'
}
const rolePermissions: Record<User['role'], Permission[]> = {
  admin: ['read', 'write', 'delete', 'admin'],
  moderator: ['read', 'write', 'delete'],
  user: ['read', 'write']
}
export function hasPermission(user: User, permission: Permission): boolean {
  return rolePermissions[user.role].includes(permission)
}
export function requirePermission(permission: Permission) {
  return (handler: (request: Request, user: User) => Promise<Response>) => {
    return async (request: Request) => {
      const user = await requireAuth(request)
      if (!hasPermission(user, permission)) {
        throw new ApiError(403, 'Insufficient permissions')
      }
      return handler(request, user)
    }
  }
}
// Usage - HOF wraps the handler
export const DELETE = requirePermission('delete')(
  async (request: Request, user: User) => {
    // Handler receives authenticated user with verified permission
    return new Response('Deleted', { status: 200 })
  }
)

Rate Limiting

Simple In-Memory Rate Limiter

class RateLimiter {
  private requests = new Map<string, number[]>()
  async checkLimit(
    identifier: string,
    maxRequests: number,
    windowMs: number
  ): Promise<boolean> {
    const now = Date.now()
    const requests = this.requests.get(identifier) || []
    // Remove old requests outside window
    const recentRequests = requests.filter(time => now - time < windowMs)
    if (recentRequests.length >= maxRequests) {
      return false  // Rate limit exceeded
    }
    // Add current request
    recentRequests.push(now)
    this.requests.set(identifier, recentRequests)
    return true
  }
}
const limiter = new RateLimiter()
export async function GET(request: Request) {
  const ip = request.headers.get('x-forwarded-for') || 'unknown'
  const allowed = await limiter.checkLimit(ip, 100, 60000)  // 100 req/min
  if (!allowed) {
    return NextResponse.json({
      error: 'Rate limit exceeded'
    }, { status: 429 })
  }
  // Continue with request
}

Background Jobs & Queues

Simple Queue Pattern

class JobQueue<T> {
  private queue: T[] = []
  private processing = false
  async add(job: T): Promise<void> {
    this.queue.push(job)
    if (!this.processing) {
      this.process()
    }
  }
  private async process(): Promise<void> {
    this.processing = true
    while (this.queue.length > 0) {
      const job = this.queue.shift()!
      try {
        await this.execute(job)
      } catch (error) {
        console.error('Job failed:', error)
      }
    }
    this.processing = false
  }
  private async execute(job: T): Promise<void> {
    // Job execution logic
  }
}
// Usage for indexing markets
interface IndexJob {
  marketId: string
}
const indexQueue = new JobQueue<IndexJob>()
export async function POST(request: Request) {
  const { marketId } = await request.json()
  // Add to queue instead of blocking
  await indexQueue.add({ marketId })
  return NextResponse.json({ success: true, message: 'Job queued' })
}

Logging & Monitoring

Structured Logging

interface LogContext {
  userId?: string
  requestId?: string
  method?: string
  path?: string
  [key: string]: unknown
}
class Logger {
  log(level: 'info' | 'warn' | 'error', message: string, context?: LogContext) {
    const entry = {
      timestamp: new Date().toISOString(),
      level,
      message,
      ...context
    }
    console.log(JSON.stringify(entry))
  }
  info(message: string, context?: LogContext) {
    this.log('info', message, context)
  }
  warn(message: string, context?: LogContext) {
    this.log('warn', message, context)
  }
  error(message: string, error: Error, context?: LogContext) {
    this.log('error', message, {
      ...context,
      error: error.message,
      stack: error.stack
    })
  }
}
const logger = new Logger()
// Usage
export async function GET(request: Request) {
  const requestId = crypto.randomUUID()
  logger.info('Fetching markets', {
    requestId,
    method: 'GET',
    path: '/api/markets'
  })
  try {
    const markets = await fetchMarkets()
    return NextResponse.json({ success: true, data: markets })
  } catch (error) {
    logger.error('Failed to fetch markets', error as Error, { requestId })
    return NextResponse.json({ error: 'Internal error' }, { status: 500 })
  }
}

Remember: Backend patterns enable scalable, maintainable server-side applications. Choose patterns that fit your complexity level.

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