Как подключить mongoDB к серверу?

Question

Я пытаюсь получить данные из MongoDB, при подключении к серверу .И вставленной одно значение в MongoDB как этот

> use abc 


switched to db abc 
> db.ac.insert({name:"naveen"}) 
WriteResult({ "nInserted" : 1 }) 
> show collections 
ac 
system.indexes 

И попытаться получить это значение, как этот

var express=require('express'); 
var app =express(); 
var MongoClient = require('mongodb').MongoClient; 
var assert = require('assert'); 


app.get('/',function(req,res){ 
    console.log("Connected to server."); 

    MongoClient.connect(url, function(err, db) { 
     assert.equal(null, err); 
     var collection = db.collection('ac'); 
     console.log(collection) 
     console.log("Connected correctly to server."); 
     db.close(); 
    }); 
}) 

var url = 'mongodb://localhost:27017/abc'; 


app.listen(3000,function(){ 
     console.log('server is runninngn') 
}) 

я получаю эту ошибку Зачем ?

MacBook-Pro:expressjs naveenkumar$ node index.js 
server is runninngn 
Connected to server. 
{ s: 
    { pkFactory: 
     { [Function: ObjectID] 
     index: 462263, 
     createPk: [Function: createPk], 
     createFromTime: [Function: createFromTime], 
     createFromHexString: [Function: createFromHexString], 
     isValid: [Function: isValid], 
     ObjectID: [Circular], 
     ObjectId: [Circular] }, 
    db: 
     { domain: null, 
     _events: {}, 
     _maxListeners: 10, 
     s: [Object], 
     serverConfig: [Getter], 
     bufferMaxEntries: [Getter], 
     databaseName: [Getter], 
     options: [Getter], 
     native_parser: [Getter], 
     slaveOk: [Getter], 
     writeConcern: [Getter] }, 
    topology: 
     { domain: null, 
     _events: [Object], 
     _maxListeners: 10, 
     s: [Object], 
     bson: [Getter], 
     isMasterDoc: [Getter], 
     poolSize: [Getter], 
     autoReconnect: [Getter], 
     host: [Getter], 
     port: [Getter], 
     emitOpen: false, 
     connectTimeoutMS: 30000, 
     socketTimeoutMS: 0 }, 
    dbName: 'abc', 
    options: { promiseLibrary: [Object], readConcern: undefined }, 
    namespace: 'abc.ac', 
    readPreference: { _type: 'ReadPreference', mode: 'primary', tags: undefined }, 
    raw: undefined, 
    slaveOk: true, 
    serializeFunctions: undefined, 
    internalHint: null, 
    collectionHint: null, 
    name: 'ac', 
    promiseLibrary: 
     { [Function: lib$es6$promise$promise$$Promise] 
     all: [Function: lib$es6$promise$promise$all$$all], 
     race: [Function: lib$es6$promise$promise$race$$race], 
     resolve: [Function: lib$es6$promise$promise$resolve$$resolve], 
     reject: [Function: lib$es6$promise$promise$reject$$reject] }, 
    readConcern: undefined } } 
Connected correctly to server. 
Connected to server. 
{ s: 
    { pkFactory: 
     { [Function: ObjectID] 
     index: 462263, 
     createPk: [Function: createPk], 
     createFromTime: [Function: createFromTime], 
     createFromHexString: [Function: createFromHexString], 
     isValid: [Function: isValid], 
     ObjectID: [Circular], 
     ObjectId: [Circular] }, 
    db: 
     { domain: null, 
     _events: {}, 
     _maxListeners: 10, 
     s: [Object], 
     serverConfig: [Getter], 
     bufferMaxEntries: [Getter], 
     databaseName: [Getter], 
     options: [Getter], 
     native_parser: [Getter], 
     slaveOk: [Getter], 
     writeConcern: [Getter] }, 
    topology: 
     { domain: null, 
     _events: [Object], 
     _maxListeners: 10, 
     s: [Object], 
     bson: [Getter], 
     isMasterDoc: [Getter], 
     poolSize: [Getter], 
     autoReconnect: [Getter], 
     host: [Getter], 
     port: [Getter], 
     emitOpen: false, 
     connectTimeoutMS: 30000, 
     socketTimeoutMS: 0 }, 
    dbName: 'abc', 
    options: { promiseLibrary: [Object], readConcern: undefined }, 
    namespace: 'abc.ac', 
    readPreference: { _type: 'ReadPreference', mode: 'primary', tags: undefined }, 
    raw: undefined, 
    slaveOk: true, 
    serializeFunctions: undefined, 
    internalHint: null, 
    collectionHint: null, 
    name: 'ac', 
    promiseLibrary: 
     { [Function: lib$es6$promise$promise$$Promise] 
     all: [Function: lib$es6$promise$promise$all$$all], 
     race: [Function: lib$es6$promise$promise$race$$race], 
     resolve: [Function: lib$es6$promise$promise$resolve$$resolve], 
     reject: [Function: lib$es6$promise$promise$reject$$reject] }, 
    readConcern: undefined } } 
**Connected correctly to server.** 

Пожалуйста, почему это дает ошибку

Answer 1

Если вы хотите отобразить все документы в данной коллекции код должен выглядеть так:

MongoClient.connect(url, function(err, db) { 
assert.equal(null, err); 
var collection = db.collection('ac').find({},function(err,doc){ 
    if(err) 
     throw err; 
    else{ 
     console.log(doc); 
    } 
}); 
console.log("Connected correctly to server."); 
db.close(); 
}); 

это будет печатать все документы сбор ac. В противном случае, если вы попытаетесь распечатать коллекцию, все метаданные также будут напечатаны.