graphql-resolvers

GraphQL resolvers are functions that return data for specific fields in your schema. Build efficient servers by writing typed resolver signatures, managing shared context for authentication and data sources, and using DataLoader to batch queries and reduce database calls.

DataLoader batching collects multiple single-item requests into one batch query, then caches results. Use it to prevent N+1 query problems—when a resolver fetches related data, DataLoader groups those fetches into a single database call per request cycle.

GraphQL resolvers support async functions and promises natively. Handle errors by returning partial results with error details in the response, catching exceptions in resolver logic, and implementing proper error handling in context setup for authentication and data access.

Yes, use context objects to share request-scoped data like authentication tokens, user info, and database loaders across all resolvers in a single request. Pass context when creating your GraphQL server, making it available to Query, Field, and Type resolvers.

Test resolvers by mocking context, data sources, and loaders, then calling resolvers directly with test arguments. Write tests for Query resolvers, Field resolvers on types, and verify error handling and async behavior across your resolver signatures.

Query resolvers fetch root-level data and often use DataLoader for efficiency. Field resolvers compute or fetch data for nested fields. Type resolvers determine concrete types in unions or interfaces. Use consistent typed signatures and context access across all three patterns.