GraphQL 完全指南

为什么选择 GraphQL？

GraphQL 解决了 REST API 的过度获取和获取不足问题，让客户端精确获取所需数据。

核心概念

Schema

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

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

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

type Mutation {
  createUser(name: String!, email: String!): User
  updatePost(id: ID!, title: String): Post
}

查询

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

响应

{
  "data": {
    "user": {
      "name": "John",
      "email": "john@example.com",
      "posts": [
        { "title": "Hello World" }
      ]
    }
  }
}

Apollo Server 实现

const { ApolloServer, gql } = require("apollo-server");

const typeDefs = gql`
  type Query {
    hello: String
  }
`;

const resolvers = {
  Query: {
    hello: () => "Hello world!"
  }
};

const server = new ApolloServer({ typeDefs, resolvers });
server.listen().then(({ url }) => {
  console.log(`Server ready at ${url}`);
});

数据加载

const DataLoader = require("dataloader");

const userLoader = new DataLoader(async (userIds) => {
  const users = await db.users.findAll({
    where: { id: userIds }
  });
  return userIds.map(id => users.find(u => u.id === id));
});

const resolvers = {
  Post: {
    author: (post) => userLoader.load(post.authorId)
  }
};

订阅 (实时数据)

type Subscription {
  postCreated: Post!
}

const resolvers = {
  Subscription: {
    postCreated: {
      subscribe: () => pubsub.asyncIterator(["POST_CREATED"])
    }
  }
};

最佳实践

1. 合理的 Schema 设计
2. 使用 DataLoader 避免 N+1
3. 查询复杂度限制
4. 深度限制
5. 缓存策略

总结

GraphQL 提供了灵活的 API 设计方式，适合复杂的数据需求场景。