How to Build a GraphQL API

Schema design, resolver patterns, and the N+1 fix - what tutorials leave out.

GraphQL promises to solve the over-fetching problem of REST. In practice, a naive GraphQL implementation creates a new problem: the N+1 query problem that can bring your database to its knees under real traffic. This guide covers schema design, resolver patterns, and the DataLoader pattern that makes GraphQL performant.

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Schema-First vs Code-First - Which to Choose?

Schema-first: you write the SDL manually and implement resolvers to match. Maximum control, clear contract before implementation, easier to share with frontend teams. Code-first (NestJS with @nestjs/graphql, Pothos): you write TypeScript and the schema is generated. Better refactoring support, TypeScript types match schema automatically, less duplication. Recommended for TypeScript backends where the schema doesnt need to be shared with non-TypeScript consumers.

At Valletta Software, we focus on:

Schema design: think in graphs not tables - model relationships not SQL joins

Resolvers: thin - delegate to services never put business logic in a resolver

DataLoader: batch and cache DB calls per request - mandatory not optional for any list resolver

Authentication: context-based (decode JWT in context function) - not per-resolver

Authorization: field-level with guards or custom directives - not in resolver logic

Pagination: cursor-based (Relay spec) for production - offset pagination breaks at scale

Rate limiting: query complexity analysis plus depth limiting - prevent malicious queries

The N+1 Problem and How to Fix It

Every GraphQL list resolver that doesnt use DataLoader has this bug in production.

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N+1 root cause: resolver for each list item fires a separate DB query - 100 items = 101 queries

DataLoader fix: batch all IDs single DB query distribute results - 100 items = 2 queries

Per-request caching: DataLoader caches within a single request - not across requests

@ResolveField: use for nested types - always pair with DataLoader for list fields

Persisted queries: hash-based query lookup - cache at CDN level reduce payload size

Query complexity: assign cost per field reject queries above threshold - prevents abuse

Monitoring: log resolver execution time - identify slow resolvers before users do

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How to Build a GraphQL API - With Engineers Who've Fixed the N+1 in Production

Our engineers implement DataLoader query complexity analysis and cursor-based pagination as defaults on every GraphQL API. The N+1 bug doesnt make it to staging.

Our engineers are trained in today's most powerful tools - Copilot, Claude, Cursor, and AI-assisted tooling - and use them daily to move faster without cutting corners.

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Our Node.js engineers implement DataLoader, query complexity analysis, and cursor-based pagination as defaults on every GraphQL API.

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