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. metadata {"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. issues }, { 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 Rate limiting must use a shared store such as Redis, a gateway, or the platform's native limiter. Do not use per-process in-memory counters for production APIs: they reset on deploy, split across replicas, and fail open in serverless or multi-instance environments. Keep the backend layer responsible for choosing the integration point and error shape; use api-design for the HTTP contract and security-review for abuse case review. 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