What is GraphQL?

The problem with traditional APIs (e.g., REST)

In traditional approaches such as REST, a client often has to make many separate queries to different endpoints (endpoints) to retrieve all the data it needs (the problem of “under-fetching” – retrieving too little data and the need for subsequent queries). On the other hand, a single REST endpoint may return much more data than the client currently needs (the problem of “over-fetching” – fetching redundant data). GraphQL is designed to solve these problems.

How does GraphQL work?

In GraphQL, the client sends a query (query) to the server, which describes the structure and fields of the data it expects. The GraphQL server interprets this query, retrieves data from various sources (e.g., databases, other services) and returns a response in JSON format that exactly matches the structure of the client’s query. Communication is usually done through a single endpoint (endpoint). GraphQL uses a type system (schema) to define the structure of the data available through the API.

Basic operations in GraphQL

GraphQL defines three main types of operations:

• Query: Used to read data from the server. The client specifies precisely which fields and related objects it wants to retrieve.
• Mutation (Mutation): Used to modify data on the server (create, update, delete). As in queries, the client can specify what data it wants to receive in response after mutation.
• Subscription: Allows clients to subscribe to changes in data on the server and receive real-time notifications (e.g. via WebSockets) when the data changes.

Schema and type system

Central to the GraphQL API is the schema, which defines the available data types, fields and operations (queries, mutations, subscriptions). The schema is strongly typed and serves as a contract between the client and the server. It allows for query validation and introspection (the ability for tools to automatically discover the API structure).

Benefits of using GraphQL

• Efficiency of data retrieval: The customer gets exactly the data it needs in a single request, eliminating the problems of under-fetching and over-fetching.
• Fewer network queries: Instead of multiple REST queries, a single GraphQL query is often sufficient.
• Strong typing and introspection: the schema provides a strict contract and enables automatic generation of documentation and development tools.
• Flexibility for customers: Clients (e.g., different versions of a mobile app, a web app) can independently evolve and request different data sets without modifying the backend API.
• Facilitated API evolution: Adding new fields to the schema does not break existing clients. Obsolete fields can be marked as deprecated.

Challenges and limitations of GraphQL

• Complexity of server-side implementation: GraphQL server implementation, especially handling nested queries and optimizing data retrieval (such as the N+1 problem), can be more complex than creating simple REST endpoints.
• Caching: HTTP caching mechanisms are less effective for GraphQL because all requests typically go to a single endpoint via POST. This requires more advanced client-side or server-side caching strategies.
• Monitoring and Rate Limiting: monitoring API usage and implementing rate limiting can be more difficult due to query flexibility.
• File handling: GraphQL is not designed to transfer binary files by default (although extensions and workarounds exist).

Summary

GraphQL is a powerful and flexible query language for APIs that solves many of the problems associated with traditional approaches like REST. It allows clients to specify the precise data they need, leading to more efficient communication and facilitating the development of client applications. While GraphQL server implementation can be more complex, the benefits of its flexibility and strong typing make it an increasingly popular choice for modern APIs.