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

typescript
1// ✅ Resource-based URLs
2GET    /api/markets                 # List resources
3GET    /api/markets/:id             # Get single resource
4POST   /api/markets                 # Create resource
5PUT    /api/markets/:id             # Replace resource
6PATCH  /api/markets/:id             # Update resource
7DELETE /api/markets/:id             # Delete resource
8
9// ✅ Query parameters for filtering, sorting, pagination
10GET /api/markets?status=active&sort=volume&limit=20&offset=0

Repository Pattern

typescript
1// Abstract data access logic
2interface MarketRepository {
3  findAll(filters?: MarketFilters): Promise<Market[]>
4  findById(id: string): Promise<Market | null>
5  create(data: CreateMarketDto): Promise<Market>
6  update(id: string, data: UpdateMarketDto): Promise<Market>
7  delete(id: string): Promise<void>
8}
9
10class SupabaseMarketRepository implements MarketRepository {
11  async findAll(filters?: MarketFilters): Promise<Market[]> {
12    let query = supabase.from('markets').select('*')
13
14    if (filters?.status) {
15      query = query.eq('status', filters.status)
16    }
17
18    if (filters?.limit) {
19      query = query.limit(filters.limit)
20    }
21
22    const { data, error } = await query
23
24    if (error) throw new Error(error.message)
25    return data
26  }
27
28  // Other methods...
29}

Service Layer Pattern

typescript
1// Business logic separated from data access
2class MarketService {
3  constructor(private marketRepo: MarketRepository) {}
4
5  async searchMarkets(query: string, limit: number = 10): Promise<Market[]> {
6    // Business logic
7    const embedding = await generateEmbedding(query)
8    const results = await this.vectorSearch(embedding, limit)
9
10    // Fetch full data
11    const markets = await this.marketRepo.findByIds(results.map(r => r.id))
12
13    // Sort by similarity
14    return markets.sort((a, b) => {
15      const scoreA = results.find(r => r.id === a.id)?.score || 0
16      const scoreB = results.find(r => r.id === b.id)?.score || 0
17      return scoreA - scoreB
18    })
19  }
20
21  private async vectorSearch(embedding: number[], limit: number) {
22    // Vector search implementation
23  }
24}

Middleware Pattern

typescript
1// Request/response processing pipeline
2export function withAuth(handler: NextApiHandler): NextApiHandler {
3  return async (req, res) => {
4    const token = req.headers.authorization?.replace('Bearer ', '')
5
6    if (!token) {
7      return res.status(401).json({ error: 'Unauthorized' })
8    }
9
10    try {
11      const user = await verifyToken(token)
12      req.user = user
13      return handler(req, res)
14    } catch (error) {
15      return res.status(401).json({ error: 'Invalid token' })
16    }
17  }
18}
19
20// Usage
21export default withAuth(async (req, res) => {
22  // Handler has access to req.user
23})

Database Patterns

Query Optimization

typescript
1// ✅ GOOD: Select only needed columns
2const { data } = await supabase
3  .from('markets')
4  .select('id, name, status, volume')
5  .eq('status', 'active')
6  .order('volume', { ascending: false })
7  .limit(10)
8
9// ❌ BAD: Select everything
10const { data } = await supabase
11  .from('markets')
12  .select('*')

N+1 Query Prevention

typescript
1// ❌ BAD: N+1 query problem
2const markets = await getMarkets()
3for (const market of markets) {
4  market.creator = await getUser(market.creator_id)  // N queries
5}
6
7// ✅ GOOD: Batch fetch
8const markets = await getMarkets()
9const creatorIds = markets.map(m => m.creator_id)
10const creators = await getUsers(creatorIds)  // 1 query
11const creatorMap = new Map(creators.map(c => [c.id, c]))
12
13markets.forEach(market => {
14  market.creator = creatorMap.get(market.creator_id)
15})

Transaction Pattern

typescript
1async function createMarketWithPosition(
2  marketData: CreateMarketDto,
3  positionData: CreatePositionDto
4) {
5  // Use Supabase transaction
6  const { data, error } = await supabase.rpc('create_market_with_position', {
7    market_data: marketData,
8    position_data: positionData
9  })
10
11  if (error) throw new Error('Transaction failed')
12  return data
13}
14
15// SQL function in Supabase
16CREATE OR REPLACE FUNCTION create_market_with_position(
17  market_data jsonb,
18  position_data jsonb
19)
20RETURNS jsonb
21LANGUAGE plpgsql
22AS $$
23BEGIN
24  -- Start transaction automatically
25  INSERT INTO markets VALUES (market_data);
26  INSERT INTO positions VALUES (position_data);
27  RETURN jsonb_build_object('success', true);
28EXCEPTION
29  WHEN OTHERS THEN
30    -- Rollback happens automatically
31    RETURN jsonb_build_object('success', false, 'error', SQLERRM);
32END;
33$$;

Caching Strategies

Redis Caching Layer

typescript
1class CachedMarketRepository implements MarketRepository {
2  constructor(
3    private baseRepo: MarketRepository,
4    private redis: RedisClient
5  ) {}
6
7  async findById(id: string): Promise<Market | null> {
8    // Check cache first
9    const cached = await this.redis.get(`market:${id}`)
10
11    if (cached) {
12      return JSON.parse(cached)
13    }
14
15    // Cache miss - fetch from database
16    const market = await this.baseRepo.findById(id)
17
18    if (market) {
19      // Cache for 5 minutes
20      await this.redis.setex(`market:${id}`, 300, JSON.stringify(market))
21    }
22
23    return market
24  }
25
26  async invalidateCache(id: string): Promise<void> {
27    await this.redis.del(`market:${id}`)
28  }
29}

Cache-Aside Pattern

typescript
1async function getMarketWithCache(id: string): Promise<Market> {
2  const cacheKey = `market:${id}`
3
4  // Try cache
5  const cached = await redis.get(cacheKey)
6  if (cached) return JSON.parse(cached)
7
8  // Cache miss - fetch from DB
9  const market = await db.markets.findUnique({ where: { id } })
10
11  if (!market) throw new Error('Market not found')
12
13  // Update cache
14  await redis.setex(cacheKey, 300, JSON.stringify(market))
15
16  return market
17}

Error Handling Patterns

Centralized Error Handler

typescript
1class ApiError extends Error {
2  constructor(
3    public statusCode: number,
4    public message: string,
5    public isOperational = true
6  ) {
7    super(message)
8    Object.setPrototypeOf(this, ApiError.prototype)
9  }
10}
11
12export function errorHandler(error: unknown, req: Request): Response {
13  if (error instanceof ApiError) {
14    return NextResponse.json({
15      success: false,
16      error: error.message
17    }, { status: error.statusCode })
18  }
19
20  if (error instanceof z.ZodError) {
21    return NextResponse.json({
22      success: false,
23      error: 'Validation failed',
24      details: error.errors
25    }, { status: 400 })
26  }
27
28  // Log unexpected errors
29  console.error('Unexpected error:', error)
30
31  return NextResponse.json({
32    success: false,
33    error: 'Internal server error'
34  }, { status: 500 })
35}
36
37// Usage
38export async function GET(request: Request) {
39  try {
40    const data = await fetchData()
41    return NextResponse.json({ success: true, data })
42  } catch (error) {
43    return errorHandler(error, request)
44  }
45}

Retry with Exponential Backoff

typescript
1async function fetchWithRetry<T>(
2  fn: () => Promise<T>,
3  maxRetries = 3
4): Promise<T> {
5  let lastError: Error
6
7  for (let i = 0; i < maxRetries; i++) {
8    try {
9      return await fn()
10    } catch (error) {
11      lastError = error as Error
12
13      if (i < maxRetries - 1) {
14        // Exponential backoff: 1s, 2s, 4s
15        const delay = Math.pow(2, i) * 1000
16        await new Promise(resolve => setTimeout(resolve, delay))
17      }
18    }
19  }
20
21  throw lastError!
22}
23
24// Usage
25const data = await fetchWithRetry(() => fetchFromAPI())

Authentication & Authorization

JWT Token Validation

typescript
1import jwt from 'jsonwebtoken'
2
3interface JWTPayload {
4  userId: string
5  email: string
6  role: 'admin' | 'user'
7}
8
9export function verifyToken(token: string): JWTPayload {
10  try {
11    const payload = jwt.verify(token, process.env.JWT_SECRET!) as JWTPayload
12    return payload
13  } catch (error) {
14    throw new ApiError(401, 'Invalid token')
15  }
16}
17
18export async function requireAuth(request: Request) {
19  const token = request.headers.get('authorization')?.replace('Bearer ', '')
20
21  if (!token) {
22    throw new ApiError(401, 'Missing authorization token')
23  }
24
25  return verifyToken(token)
26}
27
28// Usage in API route
29export async function GET(request: Request) {
30  const user = await requireAuth(request)
31
32  const data = await getDataForUser(user.userId)
33
34  return NextResponse.json({ success: true, data })
35}

Role-Based Access Control

typescript
1type Permission = 'read' | 'write' | 'delete' | 'admin'
2
3interface User {
4  id: string
5  role: 'admin' | 'moderator' | 'user'
6}
7
8const rolePermissions: Record<User['role'], Permission[]> = {
9  admin: ['read', 'write', 'delete', 'admin'],
10  moderator: ['read', 'write', 'delete'],
11  user: ['read', 'write']
12}
13
14export function hasPermission(user: User, permission: Permission): boolean {
15  return rolePermissions[user.role].includes(permission)
16}
17
18export function requirePermission(permission: Permission) {
19  return (handler: (request: Request, user: User) => Promise<Response>) => {
20    return async (request: Request) => {
21      const user = await requireAuth(request)
22
23      if (!hasPermission(user, permission)) {
24        throw new ApiError(403, 'Insufficient permissions')
25      }
26
27      return handler(request, user)
28    }
29  }
30}
31
32// Usage - HOF wraps the handler
33export const DELETE = requirePermission('delete')(
34  async (request: Request, user: User) => {
35    // Handler receives authenticated user with verified permission
36    return new Response('Deleted', { status: 200 })
37  }
38)

Rate Limiting

Simple In-Memory Rate Limiter

typescript
1class RateLimiter {
2  private requests = new Map<string, number[]>()
3
4  async checkLimit(
5    identifier: string,
6    maxRequests: number,
7    windowMs: number
8  ): Promise<boolean> {
9    const now = Date.now()
10    const requests = this.requests.get(identifier) || []
11
12    // Remove old requests outside window
13    const recentRequests = requests.filter(time => now - time < windowMs)
14
15    if (recentRequests.length >= maxRequests) {
16      return false  // Rate limit exceeded
17    }
18
19    // Add current request
20    recentRequests.push(now)
21    this.requests.set(identifier, recentRequests)
22
23    return true
24  }
25}
26
27const limiter = new RateLimiter()
28
29export async function GET(request: Request) {
30  const ip = request.headers.get('x-forwarded-for') || 'unknown'
31
32  const allowed = await limiter.checkLimit(ip, 100, 60000)  // 100 req/min
33
34  if (!allowed) {
35    return NextResponse.json({
36      error: 'Rate limit exceeded'
37    }, { status: 429 })
38  }
39
40  // Continue with request
41}

Background Jobs & Queues

Simple Queue Pattern

typescript
1class JobQueue<T> {
2  private queue: T[] = []
3  private processing = false
4
5  async add(job: T): Promise<void> {
6    this.queue.push(job)
7
8    if (!this.processing) {
9      this.process()
10    }
11  }
12
13  private async process(): Promise<void> {
14    this.processing = true
15
16    while (this.queue.length > 0) {
17      const job = this.queue.shift()!
18
19      try {
20        await this.execute(job)
21      } catch (error) {
22        console.error('Job failed:', error)
23      }
24    }
25
26    this.processing = false
27  }
28
29  private async execute(job: T): Promise<void> {
30    // Job execution logic
31  }
32}
33
34// Usage for indexing markets
35interface IndexJob {
36  marketId: string
37}
38
39const indexQueue = new JobQueue<IndexJob>()
40
41export async function POST(request: Request) {
42  const { marketId } = await request.json()
43
44  // Add to queue instead of blocking
45  await indexQueue.add({ marketId })
46
47  return NextResponse.json({ success: true, message: 'Job queued' })
48}

Logging & Monitoring

Structured Logging

typescript
1interface LogContext {
2  userId?: string
3  requestId?: string
4  method?: string
5  path?: string
6  [key: string]: unknown
7}
8
9class Logger {
10  log(level: 'info' | 'warn' | 'error', message: string, context?: LogContext) {
11    const entry = {
12      timestamp: new Date().toISOString(),
13      level,
14      message,
15      ...context
16    }
17
18    console.log(JSON.stringify(entry))
19  }
20
21  info(message: string, context?: LogContext) {
22    this.log('info', message, context)
23  }
24
25  warn(message: string, context?: LogContext) {
26    this.log('warn', message, context)
27  }
28
29  error(message: string, error: Error, context?: LogContext) {
30    this.log('error', message, {
31      ...context,
32      error: error.message,
33      stack: error.stack
34    })
35  }
36}
37
38const logger = new Logger()
39
40// Usage
41export async function GET(request: Request) {
42  const requestId = crypto.randomUUID()
43
44  logger.info('Fetching markets', {
45    requestId,
46    method: 'GET',
47    path: '/api/markets'
48  })
49
50  try {
51    const markets = await fetchMarkets()
52    return NextResponse.json({ success: true, data: markets })
53  } catch (error) {
54    logger.error('Failed to fetch markets', error as Error, { requestId })
55    return NextResponse.json({ error: 'Internal error' }, { status: 500 })
56  }
57}

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