What is GraphQL?

GraphQL is a query language for APIs and a runtime for executing those queries. It allows clients to request exactly the data they need, defining the structure of the response. Unlike traditional REST APIs, where endpoints are requested, GraphQL sends a query to a single endpoint, specifying the required fields.

Main concepts of GraphQL:

• Schema: Defines the data types, available operations (queries, mutations, subscriptions), and relationships between types. It is written in Schema Definition Language (SDL).
• Types: Define the structure of data. They can be scalar (String, Int, Float, Boolean, ID), custom, or container types (Lists, Non-Null).
• Queries: Used to fetch data from the server. The client specifies which fields are needed, and the server returns data only for those fields.
• Mutations: Used to modify data on the server (create, update, delete). They are similar to queries but explicitly indicate a change of state.
• Subscriptions: Allow clients to receive real-time updates as data changes on the server.

Advantages of GraphQL:

• Efficiency: The client requests only the necessary data, reducing the amount of transmitted information and preventing overfetching.
• Flexibility: The client defines the response structure, simplifying API development and evolution.
• Improved performance: Efficient data retrieval can speed up page loading.
• Strong typing: The schema provides a clearly defined contract between client and server, facilitating validation and error detection.

Example query:

query GetUser {
  user(id: "123") {
    name
    email
    posts {
      title
    }
  }
}

Example mutation:

mutation CreatePost {
  createPost(input: { title: "New Post", content: "..." }) {
    id
    title
  }
}