Node.jsとExpressでGraphQLサーバーを作成！初心者向け手順解説③

const express = require('express');
const { graphqlHTTP } = require('express-graphql');
const { buildSchema } = require('graphql');

// GraphQLスキーマの定義
const schema = buildSchema(`
  type User {
    id: Int!
    name: String!
    posts: [Post]
  }

  type Post {
    id: Int!
    title: String!
    content: String!
    author: User!
  }

  type Query {
    user(id: Int!): User
    post(id: Int!): Post
    users: [User]
    posts: [Post]
  }

  type Mutation {
    createUser(name: String!): User
    createPost(title: String!, content: String!, authorId: Int!): Post
  }
`);

// サンプルデータ
const users = [
  { id: 1, name: 'Alice' },
  { id: 2, name: 'Bob' },
  { id: 3, name: 'Charlie' },
];

const posts = [
  { id: 1, title: 'GraphQL入門', content: 'GraphQLは...', authorId: 1 },
  { id: 2, title: 'REST APIとの違い', content: 'REST APIとは...', authorId: 1 },
  { id: 3, title: 'Expressでの実装', content: 'Expressでの実装方法...', authorId: 2 },
];

// リゾルバ関数の定義
const root = {
  user: ({ id }) => users.find(user => user.id === id),
  post: ({ id }) => posts.find(post => post.id === id),
  users: () => users,
  posts: () => posts,
  createUser: ({ name }) => {
    const newUser = { id: users.length + 1, name };
    users.push(newUser);
    return newUser;
  },
  createPost: ({ title, content, authorId }) => {
    const newPost = { id: posts.length + 1, title, content, authorId };
    posts.push(newPost);
    return newPost;
  },
};

// UserとPostのリレーション設定
schema.getType('User').getFields().posts.resolve = (user) => posts.filter(post => post.authorId === user.id);
schema.getType('Post').getFields().author.resolve = (post) => users.find(user => user.id === post.authorId);

// Expressサーバーの設定
const app = express();
app.use('/graphql', graphqlHTTP({
  schema: schema,
  rootValue: root,
  graphiql: true,
}));

// サーバーの起動
app.listen(4000, () => console.log('GraphQLサーバーが http://localhost:4000/graphql で起動しました'));

{
  users {
    id
    name
    posts {
      title
    }
  }
}

{
  posts {
    id
    title
    content
    author {
      name
    }
  }
}

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

{
  post(id: 1) {
    id
    title
    content
    author {
      name
    }
  }
}

mutation {
  createUser(name: "Dave") {
    id
    name
  }
}

mutation {
  createPost(title: "GraphQLのアドバンテージ", content: "GraphQLのアドバンテージは...", authorId: 1) {
    id
    title
    content
    author {
      name
    }
  }
}