type User {
  id: ID!
  name: String!
  posts: [Post!]!
}

Типы описывают структуру данных — аналог классов/DTO.

input CreateUserInput {
  name: String!
  age: Int
}

enum Role {
  ADMIN
  USER
  GUEST
}

interface Entity {
  id: ID!
}

type User implements Entity {
  id: ID!
  name: String!
}

type Post implements Entity {
  id: ID!
  title: String!
}

Клиент может запросить id для любого, кто реализует Entity.

union SearchResult = User | Post | Comment

schema {
  query: Query
  mutation: Mutation
}

Сущности
type User {
  id: ID!
  name: String!
  role: Role!
  posts: [Post!]!
}

type Post {
  id: ID!
  title: String!
  content: String
  author: User!
  comments: [Comment!]!
}

type Comment {
  id: ID!
  text: String!
  author: User!
}

Перечисления
enum Role {
  ADMIN
  USER
  GUEST
}

Входные данные
input CreatePostInput {
  title: String!
  content: String
}

Запросы
type Query {
  user(id: ID!): User
  users: [User!]!

  post(id: ID!): Post
  posts(limit: Int, authorId: ID): [Post!]!
}

Мутации
type Mutation {
  createPost(input: CreatePostInput!): Post!
  deletePost(id: ID!): Boolean!
}

Подписки
type Subscription {
  postCreated: Post!
}

type Query {
  user(id: ID!): User
}

@Component
public class UserResolver implements GraphQLQueryResolver {
    private final UserService service;

    public UserResolver(UserService service) {
        this.service = service;
    }

    public User user(Long id) {
        return service.findById(id);
    }
}

type User {
  id: ID!
  name: String!
  email: String # новое поле
}

type User {
  id: ID!
  name: String!

  # старое поле
  username: String @deprecated(reason: "Use 'name' instead")
}

Старое:
input CreatePostInput {
  title: String!
}

Новое:
input CreatePostInput {
  title: String!
  content: String @deprecated(reason: "Use body instead")
  body: String
}

import java.util.EnumMap;
import java.util.Map;

enum Color { RED, GREEN, BLUE }

public class Task171125 {
    public static void main(String[] args) {
        Map<Color, String> map = new EnumMap<>(Color.class);
        
        map.put(Color.RED, "red");
        map.put(Color.GREEN, null);
        map.put(null, "null value");
        
        System.out.println(map.get(Color.RED));
        System.out.println(map.get(Color.GREEN));
        System.out.println(map.get(null));
        System.out.println(map.size());
    }
}

import java.util.LinkedHashMap;
import java.util.Map;

public class Task181125 {
    public static void main(String[] args) {
        Map<String, Integer> map = new LinkedHashMap<>(16, 0.75f, true);
        map.put("a", 1);
        map.put("b", 2);
        map.put("c", 3);
        
        map.get("a");
        map.get("b");
        map.put("d", 4);
        map.get("c");
        
        System.out.println(map.keySet());
    }
}

query {
  user(id: 42) {
    name
    avatar
  }
}

{
  "data": {
    "user": {
      "name": "Den",
      "avatar": "https://example.com/den.png"
    }
  }
}

Никаких “лишних” полей.

type Query {
  posts(limit: Int, authorId: ID): [Post!]!
}

query {
  posts(limit: 5, authorId: 42) {
    id
    title
  }
}

{
  "data": {
    "posts": [
      { "id": "101", "title": "GraphQL SDL" },
      { "id": "102", "title": "gRPC vs GraphQL" }
    ]
  }
}

query GetUser($id: ID!) {
  user(id: $id) {
    name
    avatar
  }
}

{
  "id": 42
}

type Mutation {
  createPost(input: CreatePostInput!): Post!
}

mutation {
  createPost(input: { title: "GraphQL", content: "SDL explained" }) {
    id
    title
  }
}

{
  "data": {
    "createPost": {
      "id": "501",
      "title": "GraphQL"
    }
  }
}

query {
  user(id: 1) {
    name
    posts(limit: 2) {
      title
      comments {
        text
      }
    }
  }
}

{
  "data": {
    "user": {
      "name": "Den",
      "posts": [
        {
          "title": "GraphQL Basics",
          "comments": [
            { "text": "Отличная статья" }
          ]
        },
        {
          "title": "SDL Tutorial",
          "comments": []
        }
      ]
    }
  }
}

Сервер не может изменить структуру ответа — она определяется клиентом.

data

errors

query {
  user(id: 1) {
    name
    posts {
      title
      likes
    }
  }
}

{
  "data": {
    "user": {
      "name": "Den",
      "posts": null
    }
  },
  "errors": [
    {
      "message": "Database timeout",
      "path": ["user", "posts"]
    }
  ]
}

{
  "data": {
    "createPost": null
  },
  "errors": [
    {
      "message": "User not authorized",
      "path": ["createPost"]
    }
  ]
}

public class Task191125 {
    public static void main(String[] args) {
        Object obj = "42";

        String result = switch (obj) {
            case Integer i -> "Number: " + i;
            case String s when s.length() > 3 -> "Long string";
            case String ignored -> "Short string";
            default -> "Unknown";
        };

        System.out.println(result);
    }
}