I have tried this in nodejs but i am getting undefined as output in my console
// Connect using a MongoClient instance
const MongoClient = require("mongodb").MongoClient;
const test = require("assert");
// Connection url
const url = "mongodb://localhost:27017";
// Database Name
const dbName = "test";
// Connect using MongoClient
const mongoClient = new MongoClient(url);
mongoClient.connect(function (err, client) {
const db = client.db(dbName);
try {
db.collection("employeeDetails")
.find({})
.toArray(function (err, res) {
console.log(res);
});
} catch (e) {
console.log(e);
} finally {
client.close();
}
});
I have data in mongodb :
How do i get my employee details in my console Any help would be appreciated
You're closing the connection before getting the results. If you print err inside toArray() along with result, you will see below error -
MongoExpiredSessionError: Cannot use a session that has ended
This is happening because the db.collection("employeeDetails")... is getting called but waits for results in callback, till then it moves ahead and since after that statement you are exiting try-catch, you enter into finally which closes the session. When the db.collection... call is processed, this session is already ended and you see this error.
You can use async await. Modify your code as below -
// Connect using a MongoClient instance
const MongoClient = require("mongodb").MongoClient;
const test = require("assert");
// Connection url
const url = "mongodb://localhost:27017";
// Database Name
const dbName = "test";
// Connect using MongoClient
const mongoClient = new MongoClient(url);
mongoClient.connect(async function (err, client) {
const db = client.db(dbName);
try {
const result = await db.collection('employeeDetails').find({}).toArray();
console.log(result);
} catch (e) {
console.log(e);
} finally {
client.close();
}
});
In the line mongoClient.connect(async function (err, client).. we're using async before the callback function and later inside, we can just get the result using -
const result = await db.collection('employeeDetails').find({}).toArray();
After this console.log will print your results correctly.
This works for me
let result = await collection(collection).find(query).toArray()
I have been trying W3schools tutorial on nodeJS with MongoDB.
When I try to implement this example in a nodeJS environment and invoke the function with an AJAX call, I got the error below:
TypeError: db.collection is not a function
at c:\Users\user\Desktop\Web Project\WebService.JS:79:14
at args.push (c:\Users\user\node_modules\mongodb\lib\utils.js:431:72)
at c:\Users\user\node_modules\mongodb\lib\mongo_client.js:254:5
at connectCallback (c:\Users\user\node_modules\mongodb\lib\mongo_client.js:933:5)
at c:\Users\user\node_modules\mongodb\lib\mongo_client.js:794:11
at _combinedTickCallback (internal/process/next_tick.js:73:7)
at process._tickCallback (internal/process/next_tick.js:104:9)
Please find below my implemented code:
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/mytestingdb";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
db.collection("customers").findOne({}, function(err, result) {
if (err) throw err;
console.log(result.name);
db.close();
});
});
Note that the error occurs whenever the execution hits:
db.collection("customers").findOne({}, function(err, result) {}
Also, note (in case it matters) that I have installed the latest MongoDB package for node JS (npm install mongodb), and the MongoDB version is MongoDB Enterprise 3.4.4, with MongoDB Node.js driver v3.0.0-rc0.
For people on version 3.0 of the MongoDB native NodeJS driver:
(This is applicable to people with "mongodb": "^3.0.0-rc0", or a later version in package.json, that want to keep using the latest version.)
In version 2.x of the MongoDB native NodeJS driver you would get the database object as an argument to the connect callback:
MongoClient.connect('mongodb://localhost:27017/mytestingdb', (err, db) => {
// Database returned
});
According to the changelog for 3.0 you now get a client object containing the database object instead:
MongoClient.connect('mongodb://localhost:27017', (err, client) => {
// Client returned
var db = client.db('mytestingdb');
});
The close() method has also been moved to the client. The code in the question can therefore be translated to:
MongoClient.connect('mongodb://localhost', function (err, client) {
if (err) throw err;
var db = client.db('mytestingdb');
db.collection('customers').findOne({}, function (findErr, result) {
if (findErr) throw findErr;
console.log(result.name);
client.close();
});
});
I encountered the same thing. In package.json, change mongodb line to "mongodb": "^2.2.33". You will need to uninstall mongodb npm by removing MongoDB Driver/ node_modules or etc , then install npm to install this version.
This resolved the issue for me. Seems to be a bug or docs need to be updated.
For those that want to continue using version ^3.0.1 be aware of the changes to how you use the MongoClient.connect() method. The callback doesn't return db instead it returns client, against which there is a function called db(dbname) that you must invoke to get the db instance you are looking for.
const MongoClient = require('mongodb').MongoClient;
const assert = require('assert');
// Connection URL
const url = 'mongodb://localhost:27017';
// Database Name
const dbName = 'myproject';
// Use connect method to connect to the server
MongoClient.connect(url, function(err, client) {
assert.equal(null, err);
console.log("Connected successfully to server");
const db = client.db(dbName);
client.close();
});
MongoClient.connect(url (err, client) => {
if(err) throw err;
let database = client.db('databaseName');
database.collection('name').find()
.toArray((err, results) => {
if(err) throw err;
results.forEach((value)=>{
console.log(value.name);
});
})
})
The only problem with your code is that you are accessing the object that's holding the database handler. You must access the database directly (see database variable above). This code will return your database in an array and then it loops through it and logs the name for everyone in the database.
Piggy backing on #MikkaS answer for Mongo Client v3.x, I just needed the async / await format, which looks slightly modified as this:
const myFunc = async () => {
// Prepping here...
// Connect
let client = await MongoClient.connect('mongodb://localhost');
let db = await client.db();
// Run the query
let cursor = await db.collection('customers').find({});
// Do whatever you want on the result.
}
I did a little experimenting to see if I could keep the database name as part of the url. I prefer the promise syntax but it should still work for the callback syntax. Notice below that client.db() is called without passing any parameters.
MongoClient.connect(
'mongodb://localhost:27017/mytestingdb',
{ useNewUrlParser: true}
)
.then(client => {
// The database name is part of the url. client.db() seems
// to know that and works even without a parameter that
// relays the db name.
let db = client.db();
console.log('the current database is: ' + db.s.databaseName);
// client.close() if you want to
})
.catch(err => console.log(err));
My package.json lists monbodb ^3.2.5.
The 'useNewUrlParser' option is not required if you're willing to deal with a deprecation warning. But it is wise to use at this point until version 4 comes out where presumably the new driver will be the default and you won't need the option anymore.
It used to work with the older versions of MongoDb client ~ 2.2.33
Option 1: So you can either use the older version
npm uninstall mongodb --save
npm install mongodb#2.2.33 --save
Option 2: Keep using the newer version (3.0 and above) and modify the code a little bit.
let MongoClient = require('mongodb').MongoClient;
MongoClient.connect('mongodb://localhost:27017', function(err, client){
if(err) throw err;
let db = client.db('myTestingDb');
db.collection('customers').find().toArray(function(err, result){
if(err) throw err;
console.log(result);
client.close();
});
});
I solved it easily via running these codes:
npm uninstall mongodb --save
npm install mongodb#2.2.33 --save
Happy Coding!
If someone is still trying how to resolve this error, I have done this like below.
const MongoClient = require('mongodb').MongoClient;
// Connection URL
const url = 'mongodb://localhost:27017';
// Database Name
const dbName = 'mytestingdb';
const retrieveCustomers = (db, callback)=>{
// Get the customers collection
const collection = db.collection('customers');
// Find some customers
collection.find({}).toArray((err, customers) =>{
if(err) throw err;
console.log("Found the following records");
console.log(customers)
callback(customers);
});
}
const retrieveCustomer = (db, callback)=>{
// Get the customers collection
const collection = db.collection('customers');
// Find some customers
collection.find({'name': 'mahendra'}).toArray((err, customers) =>{
if(err) throw err;
console.log("Found the following records");
console.log(customers)
callback(customers);
});
}
const insertCustomers = (db, callback)=> {
// Get the customers collection
const collection = db.collection('customers');
const dataArray = [{name : 'mahendra'}, {name :'divit'}, {name : 'aryan'} ];
// Insert some customers
collection.insertMany(dataArray, (err, result)=> {
if(err) throw err;
console.log("Inserted 3 customers into the collection");
callback(result);
});
}
// Use connect method to connect to the server
MongoClient.connect(url,{ useUnifiedTopology: true }, (err, client) => {
console.log("Connected successfully to server");
const db = client.db(dbName);
insertCustomers(db, ()=> {
retrieveCustomers(db, ()=> {
retrieveCustomer(db, ()=> {
client.close();
});
});
});
});
I have MongoDB shell version v3.6.4, below code use mongoclient, It's good for me:
var MongoClient = require('mongodb').MongoClient,
assert = require('assert');
var url = 'mongodb://localhost:27017/video';
MongoClient.connect(url,{ useNewUrlParser: true }, function(err, client)
{
assert.equal(null, err);
console.log("Successfully connected to server");
var db = client.db('video');
// Find some documents in our collection
db.collection('movies').find({}).toArray(function(err, docs) {
// Print the documents returned
docs.forEach(function(doc) {
console.log(doc.title);
});
// Close the DB
client.close();
});
// Declare success
console.log("Called find()");
});
MongoDB queries return a cursor to an array stored in memory. To access that array's result you must call .toArray() at the end of the query.
db.collection("customers").find({}).toArray()
Late answer but maybe someone will need it in future
we can create async function which one will return our collection and db instances
const dBInstances = async () => {
const collection = await db
.then((client) => {
const db = client.db();
const collection = db.collection("AGGREGATION");
return { collection: collection, db: db };
})
.catch((err) => {
console.log(`Data base instances error ${err}`);
});
return collection;
};
and after we can use result of execution dBInstances() by this way i used JS destructurisation in example below
const test = async (req, res) => {
const { collection, db } = await dBInstances();
console.log(collection);
console.log(db);
};
now we have separated access to our db and collection.
Recently I had the same issue, I finally resolved it using MongoDB official website documentation and sample codes.
My MongoDB client version is "mongodb": "^4.4.1" and I managed to insert a document finally without needing to downgrade my MongoDB package according to the approved answer which seems to be obsolete.
import { MongoClient } from "mongodb";
// Replace the uri string with your MongoDB deployment's connection string.
const uri = "<connection string uri>";
const client = new MongoClient(uri);
async function run() {
try {
await client.connect();
const database = client.db("insertDB");
const haiku = database.collection("haiku");
// create a document to insert
const doc = {
title: "Record of a Shriveled Datum",
content: "No bytes, no problem. Just insert a document, in MongoDB",
}
const result = await haiku.insertOne(doc);
console.log(`A document was inserted with the _id: ${result.insertedId}`);
} finally {
await client.close();
}
}
run().catch(console.dir);
I want to query last 10 elements in Mongodb and return elements in this query for render to index.ejs I try a lot of way for this for example (callback,asyc function) but I can't fix this problem
function getlastelements(ID){
var MongoC = mongodb.MongoClient;
var url = 'mongodb://localhost:27017/Weatherdb';
MongoC.connect(url, function(err,db){
var collection = db.collection('datas');
collection.find({"ID" : String(ID)}).sort({_id:-1}).limit(10),(function(err,cursor){
var xyz = cursor.toArray();
return(xyz.length);
})
});
}
console.log(getlastelements(1));
Your function can return a promise on which you can call the .then() method to get the value (also, remember to close the db at the end of the function)
var mongodb = require('mongodb')
function getlastelements(ID){
return new Promise(function(resolve, reject){
var MongoC = mongodb.MongoClient;
var url = 'mongodb://localhost:27017/Weatherdb';
MongoC.connect(url, function(err,db){
var collection = db.collection('datas');
collection.find({"ID" : String(ID)}).sort({_id:-1}).limit(10)
.toArray(function(err, cursor){
if(err) reject(err)
resolve(cursor.length)
db.close()
})
})
});
}
getlastelements(1).then(result => console.log(result)).catch(err => console.log(err)
Javascript Promises
I would like to connect to mongodb first, then run everything else in my application.
To do it I have to write something like:
MongoClient.connect("mongodb://localhost/test", function(err, connection) {
if (err) { console.error(err); }
db = connection;
var app = express();
// Include API V1
require("./apiv1.js")(app, db);
app.listen(3000, function(err) {
if (err) { console.error(err); } else { console.log("Started on *:3000"); }
});
});
This makes my app to be completely indented inside the .connect function... Which looks ugly and takes space while I work on my project.
I think the best solution would be have the MongoDB connection synchronous (even because witout the DB connection my app cannot work so why should I do something while it's connecting?) and then run the rest of my code.
How can I do?
You can't connect to MongoDB synchronously, but you may get rid of this ugly callback from your code.
The best way to do it is to adopt some wrapper around node-mongodb-native driver.
Take a look at the following modules.
mongojs
var mongojs = require('mongojs');
var db = mongojs('localhost/test');
var mycollection = db.collection('mycollection');
mongoskin
var mongo = require('mongoskin');
var db = mongo.db("mongodb://localhost:27017/test", {native_parser:true});
monk
var monk = require('monk');
var db = monk('localhost/test');
var users = db.get('users')
Of course, internally all of them are establishing MongoDB connection asynchronously.
Using the async library, you can aleve some of these issues.
For example in my server startup I do the following :
async.series([
function(callback){
// Initialize the mongodb connection and callback on completion in init.
db.init(function(){
callback();
});
},
function(callback){
// Listen on requests etc.
webServer.init(function(){
callback();
});
},
function(callback){
// Set up anything else that I need
callback();
}
]);
If you are using Node 6 and up versions, you can do something like this:
const MongoClient = require('mongodb').MongoClient;
const url = 'mongodb://localhost:27017/mydb';
let db = null;
getdb();
//your code
async function getdb() {
db = await MongoClient.connect(url);
}
Bring the mongodb library.
Declare the url constant .
Declare the variable db as null.
Call the getdb function.
Create the getdb function which has firt the async word
Assign to the db variable the result of the connection with the key word await.
You can do it with thunky, thunky executes an async function once and caches it, the subsequent calls are returned from the cache.
const MongoClient = require('mongodb').MongoClient;
const thunky = require('thunky');
var connect = thunky(function(cb){
let url = 'mongodb://localhost:27017/test';
MongoClient.connect(url, function(err, client){
console.log('connecting')
cb(err, client);
})
})
connect( (err, client) => {
console.log('connection 1')
})
connect( (err, client) => {
console.log('connection 2')
})
connect( (err, client) => {
console.log('connection 3')
console.log('closing')
client.close();
})
*Note: I am using latest 3.x mongodb driver
how do i share the db object returned from when i call db.open or db.connect across the entire app?
i have a dbconnect.js module as follows :
var mongodb = require('mongodb');
var global_db = '';
// Define options. Note poolSize.
var serverOptions = {
'auto_reconnect': true,
'poolSize': 5
};
// Now create the server, passing our options.
var serv = new mongodb.Server('localhost', 27017, serverOptions);
// At this point, there is no connection made to the server.
// Create a handle to the Mongo database called 'myDB'.
var dbManager = new mongodb.Db('myDB', serv);
// NOW we initialize ALL 5 connections:
dbManager.open(function (error, db) {
// Do something with the connection.
global_db = db;
// Make sure to call db.close() when ALL connections need
// to be shut down.
db.close();
});
function getConnection()
{
return global_db;
}
exports.getConnection = getConnection;
and i am using this dbconnect.js in my app.js as:
var http = require('http');
var db = require('./dbconnect').getConnection();
var collection = db.collection('testcollection');
console.log(db);
console.log(collection);
var server = http.createServer();
server.on('request',route);
server.listen(8000,'127.0.0.1');
console.log('Server running at http://127.0.0.1:8000');
function route(request,response)
{
var url = request.url;
var doc = {};
doc[url] = 'ok';
collection.insert(doc,{w:1},function(err,result)
{
if(err) console.log(err);
else console.log(result);
});
}
in the console, the db and collection variable show empty values, i also tried removing the db.close() call in dbconnect.js but to no use, however the insertion works when i place it inside dbconnect.js file in the dbManager.open function, how do i do this?or any similar alternatives?
You can't do that, because dbManager.open( is async method, but you trying to get data from module synchronously.
Try this:
In dbconnect.js
var on_db_ready = null;
module.exports = {
db_ready:function(db_ready_callback){
on_db_ready = db_ready_callback;
//here we call callback if already have db
if (global_db) on_db_ready(global_db);
},
getConnection:getConnection
};
dbManager.open(function (error, db) {
if (on_db_ready) on_db_ready(db);
global_db= db;
})
in app.js:
var db = require('./dbconnect').db_ready(function(db){
//Here i have my database
//or can use getConnection method
});
this is not very beautiful way, but, I hope, explain your mistake