GraphQL：Node.js代码实现简单例子

盛夏的果实

GraphQL 是一种针对 Graph（图状数据）进行查询特别有优势的 Query Language（查询语言）

　　文档：
国内：https://graphql.cn/
国外：https://graphql.org/

一、一个简单的例子
　　文档：https://graphql.cn/graphql-js/
　　依赖

npm i --save graphql

　　示例

var { graphql, buildSchema } = require('graphql');
// 使用 GraphQL schema language 构建一个 schema
var schema = buildSchema(`
  type Query {
  hello: String
  }
`);
// 根节点为每个 API 入口端点提供一个 resolver 函数
var root = {
  hello: () => {
  return 'Hello world!';
  },
};
// 运行 GraphQL query '{ hello }' ，输出响应
graphql(schema, '{ hello }', root).then((response) => {
  console.log(response);
});

二、整合Express提供API服务
　　依赖

npm i --save express  express-graphql graphql cors axios

　　服务端 server.js

const express = require("express");
const cors = require("cors"); // 用来解决跨域问题
const { graphqlHTTP } = require("express-graphql");
const { buildSchema } = require("graphql");
// 创建 schema
// 1. 感叹号 ！ 代表 not-null
const schema = buildSchema(`
  type Query {
  username: String
  age: Int!
  }
`);

//定义服务端数据
const root = {
  username: () => {
  return "李华";
  },
  age: () => {
  return Math.ceil(Math.random() * 100);
  },
};
const app = express();
app.use(cors());
app.use("/graphql", graphqlHTTP({
  schema: schema,
  rootValue: root,
  graphiql: true,  // 启用GraphiQL
  })
);
app.listen(3300, ()=>{
  console.log("Running a GraphQL API server at http://localhost:3300/graphql");
});

　　可视化地址：http://localhost:3300/graphql
　　客户端 client.js

const axios = require("axios");
let data = {
  query: '{username, age}'
}
axios.post("http://localhost:3300/graphql", data).then((res) => {
  console.log(res.data.data);
});
// { username: '李华', age: 26 }

　　参考
我为什么放弃RESTful，全面拥抱GraphQL
GraphQL一个简单的入门示例
GraphQL示例代码

三、看一个复杂一点的例子
　　用户User - 博客Blog - 地址Address 三者存在的一对一，一对多关系
　　服务端代码

var express = require("express");
var { graphqlHTTP } = require("express-graphql");
var {
  GraphQLSchema,
  GraphQLObjectType,
  GraphQLID,
  GraphQLString,
  GraphQLInt,
  GraphQLList,
} = require("graphql");
// 博客
var Blog = new GraphQLObjectType({
  name: "Blog",
  fields: {
  id: { type: GraphQLID },
  title: { type: GraphQLString },
  content: { type: GraphQLString },
  created_time: { type: GraphQLInt },
  },
});
// 地址
var Address = new GraphQLObjectType({
  name: "Address",
  fields: {
  id: { type: GraphQLID },
  name: { type: GraphQLString },
  },
});
// 用户 User 一对一 Address, User 一对多 Blog
var User = new GraphQLObjectType({
  name: "User",
  fields: {
  id: { type: GraphQLID },
  username: { type: GraphQLString },
  password: { type: GraphQLString },
  address: {
    type: Address,
    resolve(parent, args) {
    console.log(parent, args);
    return {
      id: parent.id,
      name: "name" + parent.id,
    };
    },
  },
  blogs: {
    type: new GraphQLList(Blog),
    args: {
    limit: { type: GraphQLInt },
    },
    resolve(parent, args) {
    console.log(parent, args);
    let list = [];
    for (let i =0; i < args.limit; i++) {
      list.push({
      id: i,
      title: "title" + i,
      content: "content" + i,
      created_time: i * 100,
      });
    }
    return list;
    },
  },
  },
});
var Query = new GraphQLObjectType({
  name: "Query",
  fields: {
  user: {
    type: User,
    args: {
    id: { type: GraphQLID },
    },
    resolve(parent, args) {
    console.log(parent, args);
    return {
      id: args.id,
      username: "admin" + args.id,
      password: "123456" + args.id,
    };
    },
  },
  },
});
var schema = new GraphQLSchema({
  query: Query,
});
//  express服务
var app = express();
app.use(
  "/graphql",
  graphqlHTTP({
  schema: schema,
  graphiql: true,
  })
);
app.listen(4000, () => {
  console.log("server at: http://localhost:4000/graphql");
});

　　客户端请求

const axios = require("axios");
let query = `
  {
  user(id: 3) {
    id
    username
    password
    blogs(limit: 2) {
    id
    title
    content
    created_time
    }
    address {
    id
    name
    }
  }
  }
`
axios.post("http://localhost:4000/graphql", {query}).then((res) => {
  console.log(res.data.data);
});
/**
{ user:
  { 
  id: '3',
  username: 'admin3',
  password: '1234563',
  blogs: [ [Object], [Object] ],
  address: { id: '3', name: 'name3' } 
  } 
}
 */