APIs (REST vs. GraphQL)

Overview

APIs (Application Programming Interfaces) define how clients and servers communicate. REST and GraphQL are two popular approaches for building web APIs.

REST (Representational State Transfer) is an architectural style using standard HTTP methods and multiple endpoints. GraphQL is a query language allowing clients to request exactly what data they need through a single endpoint.

Key Concepts

REST

Resource-based API using HTTP methods. Each resource has its own URL endpoint (e.g., /users, /posts). Returns fixed data structures.

GraphQL

Query-based API with a single endpoint. Clients specify exactly what data they want. Returns precisely requested data structure.

Endpoints

REST uses multiple endpoints (/users, /posts). GraphQL uses one endpoint (/graphql) with different queries.

How It Works

REST Example: GET /api/users/123 GET /api/users/123/posts GET /api/posts/456/comments

Each endpoint returns predefined data structure. Need 3 requests for user, their posts, and post comments.

GraphQL Example: POST /graphql Body: { user(id: 123) { name posts { title comments { text } } } }

Single request, gets exact data needed.

Use Cases

REST: Public APIs, simple CRUD operations, microservices communication

REST: Mobile apps with limited bandwidth (can cache individual resources)

GraphQL: Complex data requirements with nested relationships

GraphQL: Mobile apps wanting to minimize data transfer

GraphQL: Rapid frontend development with changing requirements

Best Practices

REST: Use nouns for resources (/users, not /getUsers)

REST: HTTP methods: GET (read), POST (create), PUT (update), DELETE (remove)

REST: Version your API (/api/v1/)

REST: Use proper status codes

GraphQL: Implement query complexity limits

GraphQL: Use DataLoader to prevent N+1 query problems

Both: Implement authentication and authorization

Both: Use pagination for large datasets

Both: Provide clear documentation

Interview Tips

What Interviewers Look For

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Compare REST vs GraphQL trade-offs based on use case
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Discuss over-fetching/under-fetching problems in REST
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Explain how GraphQL solves the N+1 query problem with DataLoader
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Talk about caching: REST easier, GraphQL needs custom solutions
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Mention when to use each: REST for simple/public APIs, GraphQL for complex data needs
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Know RESTful principles: stateless, cacheable, uniform interface