GraphQL revolutionized how apps consume APIs. Instead of fixed endpoints, the client requests exactly the data it needs. This guide presents GraphQL, comparison with REST and how to implement it in mobile apps.
What is GraphQL
Definition
Query language for APIs developed by Facebook.
Concept
Client defines response structure, not the server.
Schema
Typed contract that defines available data.
GraphQL vs REST
Over-fetching
REST returns fixed data. GraphQL returns only the order.
Under-fetching
REST may require multiple calls. GraphQL in a query.
Flexibility
Customer controls what they receive.
Versioning
GraphQL evolves schema without API versions.
Fundamental Concepts
Query
Fetch data. Read operations.
Mutation
Modify data. Write operations.
Subscription
Real-time data via WebSocket.
Schema
Definition of types and operations.
Solve
Function that fetches data for each field.
Advantages for Mobile
Data Economy
Fewer bytes transferred.
Less Latency
One call vs multiple.
Offline First
Smartest cache possible.
Typing
Schema as contract. Code generation.
Backend implementation
GraphQL Servers
Apollo Server, GraphQL Yoga, Hasura.
Schema Design
Model domain, not database.
Resolvers
Fetch data from any source.
###DataLoader
Batching to avoid n+1 queries.
Mobile Clients
###ApolloClient
iOS, Android, React Native. Feature-rich.
Relay
Facebook. Opinionated, optimized.
GraphQL Request
Take it. For simple cases.
Code Generation
Types generated from the schema. Type safety.
Query Language
Fields
Specify exactly what you want.
Arguments
Filter and customize.
Aliases
Rename fields in the response.
Fragments
Reuse selections.
Variables
Dynamic parameters.
Mutations
Syntax
Similar to query, but to modify.
Input Types
Complex objects as a parameter.
Response
Return updated data.
Optimistic Update
UI updates before response.
Subscriptions
Use Cases
Chat, notifications, real-time feeds.
Transport
WebSocket, SSE.
Caching
Automatically updates cache.
Caching
Normalized Cache
Entities stored by ID.
Fetch Policies
cache-first, network-only, cache-and-network.
Invalidation
Update cache after mutations.
Persistence
Persistent cache for offline.
##Performance
Query Complexity
Limit depth and complexity.
Pagination
Cursor-based for large lists.
Persisted Queries
Hash instead of full string.
CDN
Edge caching for public queries.
Security
Authentication
Token in the header.
Authorization
Validate permissions on resolvers.
Rate Limiting
By operation, not endpoint.
Query Depth
Limit depth to prevent abuse.
Error Handling
Partial Success
GraphQL may return data and errors.
Error Types
Customize by error type.
Client Handling
Handle mistakes gracefully.
Tooling
###GraphiQL/Playground
Interface to explore schema.
Code Generators
graphql-codegen. Automatic types.
Apollo Studio
Monitoring, schema registry.
Linting
eslint-plugin-graphql.
REST migration
Gradual
Add GraphQL next to REST.
Federation
Multiple services GraphQL united.
Wrapping
GraphQL in front of existing REST.
Best Practices
Schema First
Define schema before implementing.
Naming
Clear conventions. PascalCase types, camelCase fields.
Documentation
Descriptions in the schema.
Deprecation
Mark obsolete fields.
When to Use GraphQL
Good For
- Mobile apps with complex data
- Multiple different clients
- Rapid product iteration
Not Ideal For
- Simple APIs
- Heavy file upload
- Intensive real-time (consider gRPC)
Conclusion
GraphQL is powerful for mobile apps that need efficiency and flexibility. Learn the concepts, choose the appropriate stack and implement it with discipline. The result is faster apps and more productive development.
##FAQs
1) GraphQL replaces REST? Not necessarily. Each has use cases. They can coexist.
2) Is GraphQL slower than REST? Not inherently. It depends on implementation.
3) Do I need to rewrite the backend? No. GraphQL can wrap existing services.
4) Mobile specific or does it work for the web? Works for any client. Mobile benefits a lot.
5) Is Apollo mandatory? No. It's popular but there are alternatives.
Also read
- Modern GraphQL APIs: Schema Design, Performance, and Patterns that Work
- GraphQL in applications: costs, prices and a checklist before adopting
- Backend for Applications: Architecture, Technologies and Best Practices
- Microservices in Applications: Distributed Architecture for Mobile
- GraphQL for Applications: Costs and Pricing with Real Cases
- API For Applications