快速上手使用express-graphql 构建graphql 查询接口

直接上代码
```
const express = require('express')
const {buildSchema} = require('graphql')
const {graphqlHTTP} = require('express-graphql')

const schema = buildSchema(`
    type Student{
        name:String
        sex:String
        age:Int
        is_test: Boolean
        otherInfo(type:String):String
    }

type Query{
        getClassInfo(classNo: Int!):[String] 
        getStudents(classNo: Int!):Student 
    }
`)

const root = {
    //需要返回[String] 字符串数组类型
    getClassInfo({classNo}){
        const obj = {
            1:["A","B","C"],
            2:["F","G","H"]
        }
        return obj[classNo]
    },
    getStudents({classNo}){
        const obj={
            1:{"name":"张三","age":18,"sex":"男","is_test":true,"otherInfo":""},
            2:{"name":"李四","age":88,"sex":"女","is_test":false,"otherInfo":""}
        }
        const otherInfo = ({type}) => {
            if(type == "new"){
                return "新班级";
            }
            else{
                return "旧班级"
            }
        }
        const newobj = obj[classNo]
        newobj.otherInfo = otherInfo
        return newobj
    }
}

const app = express();

app.use('/g',graphqlHTTP({
    schema: schema,
    rootValue: root,
    graphiql: true  //是否调试模式，dev模式下开启
}))

app.listen(3000);

```
保存为test.js
初如化package.json
```
cnpm init -y
```
安装依赖包
```
cnpm i express-graphql graphql express -S
```
运行项目：
```
node test.js
```

重点说明：
1、graphqlHTTP 需要传入三个参数，
2、schema和root 中的方法 一一对应。
3、Int!  加叹号为必传值 
4、Student 结构 为自定义数据类型
5、otherInfo 带参，对应需要定义箭头函数

测试查询地址：
```
http://localhost:3000/g?query=%23%20Welcome%20to%20GraphiQL%0A%23%0A%23%20GraphiQL%20is%20an%20in-browser%20tool%20for%20writing%2C%20validating%2C%20and%0A%23%20testing%20GraphQL%20queries.%0A%23%0A%23%20Type%20queries%20into%20this%20side%20of%20the%20screen%2C%20and%20you%20will%20see%20intelligent%0A%23%20typeaheads%20aware%20of%20the%20current%20GraphQL%20type%20schema%20and%20live%20syntax%20and%0A%23%20validation%20errors%20highlighted%20within%20the%20text.%0A%23%0A%23%20GraphQL%20queries%20typically%20start%20with%20a%20%22%7B%22%20character.%20Lines%20that%20start%0A%23%20with%20a%20%23%20are%20ignored.%0A%23%0A%23%20An%20example%20GraphQL%20query%20might%20look%20like%3A%0A%23%0A%23%20%20%20%20%20%7B%0A%23%20%20%20%20%20%20%20field(arg%3A%20%22value%22)%20%7B%0A%23%20%20%20%20%20%20%20%20%20subField%0A%23%20%20%20%20%20%20%20%7D%0A%23%20%20%20%20%20%7D%0A%23%0A%23%20Keyboard%20shortcuts%3A%0A%23%0A%23%20%20Prettify%20Query%3A%20%20Shift-Ctrl-P%20(or%20press%20the%20prettify%20button%20above)%0A%23%0A%23%20%20%20%20%20Merge%20Query%3A%20%20Shift-Ctrl-M%20(or%20press%20the%20merge%20button%20above)%0A%23%0A%23%20%20%20%20%20%20%20Run%20Query%3A%20%20Ctrl-Enter%20(or%20press%20the%20play%20button%20above)%0A%23%0A%23%20%20%20Auto%20Complete%3A%20%20Ctrl-Space%20(or%20just%20start%20typing)%0A%23%0A%0Aquery%7B%0A%20%20getClassInfo(classNo%3A1)%0A%20%20getStudents(classNo%3A1)%20%7B%0A%20%20%20%20name%0A%20%20%20%20sex%0A%20%20%20%20age%0A%20%20%20%20is_test%0A%20%20%20%20otherInfo(type%3A%22new%22)%0A%20%20%7D%0A%7D
```

快速上手使用express-graphql 构建graphql 查询接口

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