GraphQL vLatestINTERMEDIATEGraphQL
Complete guide to GraphQL - query language and runtime for APIs with types, queries, mutations, and subscriptions
15 min read
graphqlapiqueriesmutationssubscriptionsapolloschemaresolvers
Table of Contents
Setup & Basics
GraphQL Server Setup
📄 Codejavascript
💡 GraphQL is a query language and runtime for APIs
⚡ Single endpoint typically at /graphql
📌 Strongly typed with schema definition
🟢 Works with any backend language or database
Schema Definition Language (SDL)
📄 Codegraphql
💡 Schema defines API structure and types
⚡ ! means non-nullable, [] means list
📌 Scalar types: Int, Float, String, Boolean, ID
🔥 Custom scalars for dates, JSON, etc.
Queries
Basic queries
graphql
💡 Request exactly what you need
⚡ Single request for nested data
📌 No over-fetching or under-fetching
🟢 Predictable results matching query shape
Query variables and directives
graphql
💡 Variables make queries reusable
⚡ Directives modify query execution
📌 @include and @skip for conditional fields
🔥 Custom directives for advanced features
Mutations
Basic mutations
graphql
💡 Mutations modify server-side data
⚡ Return updated data after mutation
📌 Use input types for complex arguments
🟢 Can include queries in response
Optimistic updates and error handling
📄 Codejavascript
💡 Optimistic UI updates for better UX
⚡ Rollback on error automatically
📌 Error handling with try-catch
🔥 Cache updates after mutations
Subscriptions
Real-time subscriptions
javascript
💡 Real-time updates via WebSocket
⚡ Server pushes updates to clients
📌 Use for live features like chat
🔥 Efficient for selective updates
Resolvers
Resolver structure and context
javascript
💡 Resolvers fetch data for schema fields
⚡ Four arguments: parent, args, context, info
📌 Context shares data across resolvers
🟢 Can be sync or async functions
DataLoader and N+1 problem
📄 Codejavascript
💡 DataLoader batches and caches requests
⚡ Solves N+1 query problem
📌 Automatic request deduplication
🔥 Per-request caching
Authentication & Authorization
Authentication patterns
javascript
💡 Use context for auth state
⚡ JWT tokens common for GraphQL
📌 Check auth in resolvers or middleware
🔐 Never expose sensitive fields
Error Handling
Error types and handling
javascript
💡 GraphQL returns 200 OK even with errors
⚡ Errors in errors array, data can be partial
📌 Use custom error classes for clarity
🔥 Format errors for production
Performance Optimization
Query optimization techniques
javascript
💡 Use DataLoader for batching
⚡ Implement query depth limiting
📌 Add query complexity analysis
🔥 Cache with Redis or in-memory
Testing
Testing GraphQL APIs
javascript
💡 Test resolvers in isolation
⚡ Use test server for integration tests
📌 Mock data sources and context
🟢 Test both success and error cases
Best Practices
Schema design principles
graphql
💡 Design schema for clients, not database
⚡ Use clear, consistent naming
📌 Avoid deep nesting (max 3-4 levels)
🎯 Version via field deprecation, not versions
Security best practices
📄 Codejavascript
🔐 Always validate and sanitize inputs
⚡ Implement rate limiting
📌 Disable introspection in production
🔥 Use query depth and complexity limits