backend-patterns

name	backend-patterns
description	Backend architecture patterns, API design, database optimization, and server-side best practices for Node.js, Express, and Next.js API routes. Use when building or reviewing Node.js, Express, or Next.js API routes and their data access.

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)
    }

     (filters?.) {
      query = query.(filters.)
    }

     { data, error } =  query

     (error)   (error.)
     data
  }

  
}

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. === b.)?. || 
       scoreA - scoreB
    })
  }

    () {
    
  }
}

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 $$
BEGIN
  -- Start transaction automatically
  INSERT INTO markets VALUES (market_data);
  INSERT INTO positions VALUES (position_data);
  RETURN jsonb_build_object('success', true);
EXCEPTION
  WHEN OTHERS THEN
    --  happens automatically
     (, , , );
;
$$;

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(: ): <> {
     ..()
  }
}

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.
    }, { :  })
  }

  
  .(, error)

   .({
    : ,
    : 
  }, { :  })
}


   () {
   {
     data =  ()
     .({ : , data })
  }  (error) {
     (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 (token)
}


   () {
   user =  (request)

   data =  (user.)

   .({ : , 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<>) => {
      (: ) => {
       user =  (request)

       (!(user, permission)) {
          (, )
      }

       (request, user)
    }
  }
}


   = ()(
   (: , : ) => {
    
      (, { :  })
  }
)

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: ) {
   ip = request..() || 

   allowed =  limiter.(ip, , )  

   (!allowed) {
     .({
      : 
    }, { :  })
  }

  
}

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): <> {
    
  }
}


  {
  : 
}

 indexQueue =  <>()

   () {
   { marketId } =  request.()

  
   indexQueue.({ marketId })

   .({ : , :  })
}

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, {
      ...context,
      : error.,
      : error.
    })
  }
}

 logger =  ()


   () {
   requestId = crypto.()

  logger.(, {
    requestId,
    : ,
    : 
  })

   {
     markets =  ()
     .({ : , : markets })
  }  (error) {
    logger.(, error  , { requestId })
     .({ :  }, { :  })
  }
}

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