backend-patterns

# 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 // 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 ```typescript // Abstract data access logic interface MarketRepository { findAll(filters?: MarketFilters): Promise findById(id: string): Promise create(data: CreateMarketDto): Promise update(id: string, data: UpdateMarketDto): Promise delete(id: string): Promise } class SupabaseMarketRepository implements MarketRepository { async findAll(filters?: MarketFilters): Promise { 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 ```typescript // Business logic separated from data access class MarketService { constructor(private marketRepo: MarketRepository) {} async searchMarkets(query: string, limit: number = 10): Promise { // 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 ```typescript // 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.sta