backend-patterns

Backend Development Patterns

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

API Design Patterns

RESTful API Structure

// ✅ 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

// ✅ 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

// ✅ 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)

// ❌ BAD: Select everything const { data } = await supabase .from('markets') .select('*')

N+1 Query Prevention

// ❌ BAD: N+1 query problem const markets = await getMarkets() for (const market of markets) { market.creator = await getUser(market.creator_id) // N queries }

// ✅ 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 &#x3C; 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 &#x3C; 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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