“ReferenceError：数据库未定义”我找不到我的错误

Question

这是错误信息：

ReferenceError: 未定义数据库 在 /Users/dspatiyal/Desktop/Mongo DB/index.js:12:21 在 /usr/local/lib/node_modules/mongodb/lib/utils.js:731:5

这是代码：

var MongoClient= require("mongodb").MongoClient;
var url="mongodb://localhost:27017/employees";

MongoClient.connect(url, function(err,db){

    if(err){
        console.log("Error Creating Connection");
        return
    }
    console.log("Database Created Successfully..")

    var myDatabase= database.db("employees");

    myDatabase.createCollection("employeeList",function(err,res){
        if(err){
            console.log("Error Creating Connection");
            return;
        }

        var employeeListCollection=myDatabase.collection("employeeList")
        employeeListCollection.insertOne({
            name:"Utkarsh",
            age:10
        },function(err ,success){
            if(err){
                console.log("Error Creating Connection");
                return;
            }

            employeeListCollection.find({name:"Mayank"}).toArray(function(err,result){
                console.dir(result);
                database.close();
            })

            employeeListCollection.deleteOne,({name:"Mayank"},function(err,obj){
                console.log("Object Deleted...")
                database.close();
            })

            employeeListCollection.updateOne({name: "Utkarsh"},{$set :{age:1000}},function(err,result){
                database.close();
            })

            console.log("Document Added to database collection");

        })
    })

})

Answer 1

MongoClient.connect() 是异步的。在您执行var myDatabase= database.db("employees"); 时，数据库连接可能尚未准备好 看看这个post。