Node.js Graphql查询始终返回null
我试图使用graphql获取课程数据,但服务器总是返回Node.js Graphql查询始终返回null,node.js,express,graphql,express-graphql,Node.js,Express,Graphql,Express Graphql,我试图使用graphql获取课程数据,但服务器总是返回null作为响应这是我在文件server.js中的代码: var express=require('express'); const { graphqlHTTP } = require('express-graphql') var {buildSchema}=require('graphql'); //graphql schema var schema=buildSchema(` type Query { course(id: In
null
作为响应这是我在文件server.js中的代码:
var express=require('express');
const { graphqlHTTP } = require('express-graphql')
var {buildSchema}=require('graphql');
//graphql schema
var schema=buildSchema(`
type Query {
course(id: Int!): Course
courses(topic:String!):[Course]
}
type Course {
id: Int
title: String
author: String
description:String
topic:String
url: String
}
`);
var coursesData = [
{
id: 1,
title: 'The Complete Node.js Developer Course',
author: 'Andrew Mead, Rob Percival',
description: 'Learn Node.js by building real-world applications with Node, Express, MongoDB, Mocha, and more!',
topic: 'Node.js',
url: 'https://codingthesmartway.com/courses/nodejs/'
},
{
id: 2,
title: 'Node.js, Express & MongoDB Dev to Deployment',
author: 'Brad Traversy',
description: 'Learn by example building & deploying real-world Node.js applications from absolute scratch',
topic: 'Node.js',
url: 'https://codingthesmartway.com/courses/nodejs-express-mongodb/'
},
{
id: 3,
title: 'JavaScript: Understanding The Weird Parts',
author: 'Anthony Alicea',
description: 'An advanced JavaScript course for everyone! Scope, closures, prototypes, this, build your own framework, and more.',
topic: 'JavaScript',
url: 'https://codingthesmartway.com/courses/understand-javascript/'
}
]
//root resolver
var root= {
course:getCourse,
courses:getCourses
};
var getCourse= function (args){
var id=args.id;
console.log("delila")
return coursesData.filter(course=>{
return course.id==id
})[0]
}
var getCourses = function(args){
if(args.topic){
var topic=args.topic;
return coursesData.filter(course=>
course.topic===topic
);
}
else return coursesData
}
//create an experess server and graphql endpoint
var app=express();
app.use('/graphql', graphqlHTTP({
schema: schema,
rootValue:root,
graphiql:true
}));
app.listen(4000,()=>console.log("delila express graphql server running on localhost 4000"))
当我转到localhost:4000/graphql
获取我正在使用的数据时
query getSingleCourse($courseID: Int !){
course(id:$courseID){
title
author
description
url
topic
}
}
{
"courseID": 3
}
但我不断得到结果null
。看图像
有人知道为什么会这样吗?服务器应该返回带有ID3
的过程,但显然我缺少了一些东西您应该首先定义函数表达式,然后使用它们。这就是原因
与函数声明不同,JavaScript中的函数表达式不会被提升。在创建函数表达式之前,不能使用它们:
看
例如
/。。。
var getCourse=函数(args){
var id=args.id;
console.log('delila');
返回coursesData.filter((课程)=>{
return course.id==id;
})[0];
};
var getCourses=函数(args){
if(args.topic){
var topic=args.topic;
返回coursesData.filter((course)=>course.topic===topic);
}否则返回课程数据;
};
//根解析器
变量根={
课程:getCourse,
课程:getCourses,
};
//...
“args”是第二个解析器fn arg