如何在 GraphQL 中制定嵌套模式

Posted 2023-03-08

【中文标题】如何在 GraphQL 中制定嵌套模式

【英文标题】：How to formulate nested schema in GraphQL

【发布时间】：2021-11-27 23:45:06

【问题描述】：

我是 GraphQL 的新手。作为实验，我运行了以下 Node.js Express 服务器：

var express = require('express');
var  graphqlHTTP  = require('express-graphql');
var  buildSchema  = require('graphql');
var schema = buildSchema(`
  type Student 
     sid: ID,
     name: String,
     subjects: [String!],
     address: Location
  
  type Location
     unit: String,
     city: String,
     country: String,
     postCode: Int
  
`);
var root =    // The root provides a resolver function for each API endpoint
  address: () => (
    city: ()=>'London'
  ),
;
var app = express();
app.use('/graphql', graphqlHTTP(
  schema: schema,
  rootValue: root,
  graphiql: true,
));
app.listen(4000);
console.log('Running a GraphQL API server at http://localhost:4000/graphql');

当我在浏览器的界面上运行以下查询时：

  address 
     city
  

我遇到了一个错误：

    "errors": [
    
      "message": "Query root type must be provided."
    
  ]

这样做的正确方法应该是什么？

【参考方案1】：

事实证明，我必须为入口点定义模式“Query”（以及可选的“Mutation”）。

var express = require('express');
var  graphqlHTTP  = require('express-graphql');
var  buildSchema  = require('graphql');

var fakeDatabase = [sid:parseInt(Math.random()*10000),
                     name:'Philip',
                     subjects:['Chemistry', 'Physics', 'Maths'],
                     address:
                           unit: 'H505',
                           city: 'London',
                           country: 'United Kingdom',
                           postCode: 33100
];

// 'Query' and 'Mutation' are special schemas defining the entry points
var schema = buildSchema(`
  type Query 
     name: String     
     sid(year: Int): ID
     subjects: [String]
     address: Location
  
  type Location
     unit: String
     city: String
     country: String
     postCode: Int
  
  type Mutation
     setName(nn: String): String
  
`);

// Each field is either a constant or a callback
var root = 
  name: ()=>fakeDatabase[0].name,
  sid: arg => (arg.year+"-"+fakeDatabase[0].sid),
  subjects: fakeDatabase[0].subjects,
  address: () => (
     city: ()=>fakeDatabase[0].address.city
  ),
  setName: arg => fakeDatabase[0].name=arg.nn; return arg.nn;
;

var app = express();
app.use('/graphql', graphqlHTTP(
  schema: schema,
  rootValue: root,
  graphiql: true,
));
app.listen(4000);
console.log('Running a GraphQL API server at http://localhost:4000/graphql');