API basics: REST vs GraphQL

REST or GraphQL; It's Not Just a Simple Choice

When it comes to designing a new API, the first question the technical team faces is: REST or GraphQL? This question isn't as simple as it seems, because the right answer depends on the type of project, the team, the scale, and even the organizational culture. In this article, we're not going to declare one side the winner; instead, we want to take a practical look at the differences in request models, advantages, and disadvantages of each so you can make an informed decision yourself.

Both approaches were created to solve a common problem: communication between client and server. But their philosophies are completely different. REST is designed based on Resources and HTTP verbs, while GraphQL is a Query Language that allows the client to specify exactly what data it needs. This fundamental difference affects everything; from caching methods to error handling and even the developer experience.

The Request Model; Where the Differences Show Themselves

To understand the difference, let's consider a real-world scenario: imagine you're building a user panel that needs to display profile information, recent orders, and the number of unread messages.

REST; Multiple Requests for One Page

In a REST architecture, you have a separate endpoint for each resource. For the mentioned page, you'll likely need these requests:

GET /api/v1/users/123
GET /api/v1/users/123/orders?limit=5
GET /api/v1/users/123/messages/unread-count

Each of these requests returns a complete response; even if the client only needs a part of it. For example, the user information request also returns fields like address, birthDate, or settings that might not be used at all. This phenomenon is known as Over-fetching.

On the other hand, if the client needs data that isn't in the current endpoint, it has to make a new request. This state is called Under-fetching. The result is that rendering a simple page sometimes requires 3 to 5 separate HTTP requests.

GraphQL; One Request, Precise Response

In GraphQL, you have a single endpoint (usually /graphql) and the client specifies exactly what data it wants with a query:

query {
  user(id: 123) {
    name
    email
    orders(limit: 5) {
      id
      total
      status
    }
    unreadMessagesCount
  }
}

The server returns exactly the requested structure; no more, no less. This means no Over-fetching and usually, all the necessary data is received with one network round-trip. For mobile applications with limited bandwidth, this advantage can be crucial.

Advantages and Disadvantages of REST

REST has been the dominant standard for API design for over two decades, and this longevity brings with it specific advantages and disadvantages.

Advantages

• Simplicity and Familiarity: Almost all developers are familiar with the concepts of GET, POST, PUT, and DELETE. The learning curve is almost zero.
• Excellent Caching: Thanks to the use of HTTP verbs and unique URLs, you can use caching at various levels (browser, CDN, server). Headers like Cache-Control and ETag work simply.
• Mature Tools: Tools like Postman, Swagger, and OpenAPI have reached full maturity and simplify documentation, testing, and monitoring.
• Predictability: The structure of URLs and HTTP methods creates a clear contract that makes debugging easier.

Disadvantages

• Over-fetching and Under-fetching: As we saw, these two problems can lead to excessive bandwidth consumption or a high number of requests.
• Difficult Versioning: When your API changes, you usually have to create a new version (/v1, /v2) and maintaining multiple versions simultaneously is costly.
• Lack of Flexibility: The client has to deal with the server's predefined structure. If a new need arises, a new endpoint must be added.

Advantages and Disadvantages of GraphQL

GraphQL was released by Facebook in 2015 and quickly gained significant popularity. But this popularity doesn't come without a cost.

Advantages

• Precise Data Request: The client has full control and receives only the data it needs. This feature is very valuable for mobile applications and the Internet of Things (IoT).
• One Round-trip: With one request, you can receive data from multiple different sources; without needing multiple parallel or sequential requests.
• Strong Typing: The GraphQL schema creates an explicit contract between client and server. Tools like GraphQL Code Generator can automatically generate TypeScript types.
• Live Documentation: Tools like GraphiQL and Apollo Studio allow developers to browse the schema and test queries live.

Disadvantages

• Caching Complexity: Because all requests are sent to a single endpoint, HTTP-level caching is almost impossible. You need to use more complex solutions like caching at the application layer or tools like Apollo Client.
• The N+1 Problem: If resolvers aren't designed properly, a simple query might send dozens of queries to the database. Tools like DataLoader are essential for solving this problem.
• Learning Curve: Concepts like Schema, Resolver, Mutation, and Subscription are complex for beginners and require training.
• Security: Because the client can construct any query, complex attacks like Query Depth Attack or Resource Exhaustion are possible. You need to set limits like maximum query depth and execution time.

Selection Criteria; REST or GraphQL for Your Project?

Now that we have a clear picture of both, let's look at practical criteria for making a decision.

When is REST the Better Choice?

1. Public and Simple API: If your API is going to be used by external developers and the data has a simple structure, REST is a safer choice. There are plenty of documentation tools and ready-made SDKs.
2. Need for Strong Caching: If you have high traffic and want to use CDN and HTTP caching, REST has the advantage due to its URL-based structure.
3. Small or Beginner Team: If your team doesn't have enough experience with GraphQL, its complexities can slow down development. REST is simpler and more predictable.
4. Internal Systems with Fixed Needs: If the clients are limited and their needs are clear, REST can be completely sufficient.

When is GraphQL the Better Choice?

1. Mobile Applications: Where bandwidth is limited and reducing response size is very important, GraphQL has a significant advantage.
2. Complex Dashboards: If different clients have different needs from similar data (e.g., an admin dashboard and a public application), GraphQL provides the necessary flexibility.
3. Microservices Architecture: GraphQL can act as an Aggregation Layer and combine data from multiple different services into a single response.
4. Rapid Frontend Development: When the frontend team works independently from the backend, GraphQL allows them to request the data they need without waiting for new endpoints.

Common Mistakes and Troubleshooting Tips

Over the years of working with both technologies, I've seen a few common mistakes repeatedly that are worth mentioning:

Common Mistake in REST: Ignoring Versioning

Many teams think API versioning means adding /v1 to the URL. But real versioning means managing breaking changes in a controlled way. If you remove a field from the response, old clients will break. A better solution is using the Accept-Version header or releasing a new version with a separate URL and maintaining the previous version in parallel.

Common Mistake in GraphQL: Ignoring N+1

Suppose you write a query to get a list of users and their orders. If the resolver for orders makes a separate query for each user, for 100 users, 101 queries will be sent to the database. The solution is to use DataLoader, which combines duplicate requests into a single batch:

const orderLoader = new DataLoader(async (userIds) => {
  const orders = await db.query(
    'SELECT * FROM orders WHERE user_id IN (?)',
    [userIds]
  );
  return userIds.map(id => orders.filter(o => o.user_id === id));
});

Troubleshooting: 4xx Errors in GraphQL

In REST, the HTTP status code has a specific meaning (404 means resource not found). In GraphQL, all responses usually return with code 200, and errors are placed in the errors section of the response. This can complicate monitoring. Make sure to implement filtering based on the presence of errors in the response in your monitoring services.

Conclusion; The Final Decision is Yours

The choice between REST or GraphQL is not a black-and-white decision. Both are powerful tools that shine in specific situations. If you're looking for simplicity, strong caching, and mature tools, REST is a safe choice. If you're looking for flexibility, reduced data volume, and a more modern developer experience, and your team is ready to embrace its complexities, GraphQL can create a significant transformation.

The important thing is that you can use both in a combined way. Many large companies have a public REST API while also using GraphQL for internal and mobile applications. Ultimately, the best choice is the one that aligns with your project's real needs, your team's skills, and your long-term strategy.

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