Compare REST and GraphQL. What are the main differences, and when would you choose one over the other?

Question

Accepted Answer

## REST Overview

REST uses multiple endpoints, each returning a fixed data structure. The server decides what data to return.

```
GET /users/123
GET /users/123/posts
GET /posts/456/comments
```

Each endpoint returns a predefined response shape.

## GraphQL Overview

GraphQL uses a single endpoint where the client specifies exactly what data it needs.

```graphql
query {
  user(id: "123") {
    name
    email
    posts {
      title
      comments {
        text
      }
    }
  }
}
```

The client gets exactly the requested fields—nothing more, nothing less.

## Key Differences

| Aspect | REST | GraphQL |
|--------|------|---------|
| **Endpoints** | Multiple endpoints | Single endpoint |
| **Data fetching** | Fixed response shape | Client specifies fields |
| **Over-fetching** | Common (server decides) | Avoided |
| **Under-fetching** | May require multiple requests | Single request possible |
| **Versioning** | URL or header versioning | Schema evolution |
| **Caching** | HTTP caching built-in | Requires custom strategies |
| **Learning curve** | Lower | Higher |
| **Tooling** | Mature ecosystem | Growing ecosystem |

## Over-fetching and Under-fetching

### Over-fetching (REST Problem)

You request a user but receive more data than needed:

```json
// You only need name and email, but you get everything.
{
  "id": 123,
  "name": "Alice",
  "email": "alice@example.com",
  "address": "...",
  "phone": "...",
  "createdAt": "...",
  "preferences": { ... }
}
```

### Under-fetching (REST Problem)

You need user data plus their posts, requiring multiple requests:

```
GET /users/123        → User data
GET /users/123/posts  → Posts data
GET /posts/1/comments → Comments for post 1
GET /posts/2/comments → Comments for post 2
```

GraphQL solves this with a single query.

## When to Choose REST

- **Simple CRUD applications** with straightforward data requirements.
- **Public APIs** where caching and predictable responses matter.
- **Teams unfamiliar with GraphQL** who need a quicker start.
- **File uploads** and binary data handling (REST handles this more naturally).
- **Microservices** where services have well-defined, stable contracts.

## When to Choose GraphQL

- **Complex data relationships** where clients need flexibility.
- **Mobile applications** that benefit from reducing network requests.
- **Rapidly evolving frontends** that frequently change data requirements.
- **Aggregating data from multiple sources** into a unified API.
- **Real-time features** using subscriptions.

## Hybrid Approach

Many teams use both:

- REST for simple, cacheable resources (images, files, authentication).
- GraphQL for complex, nested data queries.

## Summary

REST is simpler and benefits from mature tooling and caching. GraphQL offers flexibility and efficiency for complex data needs. Choose based on your application's requirements, team expertise, and performance considerations.