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Can Not Retrieve Nodejs MySQl Data From Database via sub function call

I have two files named login.js and dbMySql.js.
login.js is the main file that will run dbMySql.js, which is a submodule for the DB connection.
I can run getQuery() from dbMySql.js by using object.method call.
getQuery() also works fine and retrieves data from the database.
How can I get this data to my Main module from the database module? How can I return res variable to main function in login.js module
Code For login.js:
var MySqlConnect = require('./dbMySql');
var app = express();
var dbConnect = MySqlConnect("localhost", "root", "root", "mydb");
dbConnect.getQuery("select * from `test`");
console.log(dbConnect.resD);
Code For dbMySql.js:
function MySqlConnect(dbhost, dbuser, dbpassword, dbname) {
var MySqlConnect = require('mysql');
var con;
this.dbhost = dbhost;
this.dbuser = dbuser;
this.dbpassword = dbpassword;
this.dbname = dbname;
this.resultData = 'Def';
con = MySqlConnect.createConnection({
host: dbhost,
user: dbuser,
password: dbpassword,
database: dbname
})
con.connect(function (err) {
if (err) throw err;
})
function getQuery(query1) {
con.query(query1, function (err, res) {
if (err) throw err;
})
return {
resD: res
};
}
return {
getQuery: getQuery,
};
};
module.exports = MySqlConnect;
I want Retrieved Data in Main module via return method or any that will run successfully.

Vary Simple Answer I have found by run and execute after efforts.
just pass res form db to callback function parameter and run this fucntion from main module

mongodb: cannot define variable [duplicate]

I'm using the node-mongodb-native driver with MongoDB to write a website.
I have some questions about how to manage connections:
Is it enough using only one MongoDB connection for all requests? Are there any performance issues? If not, can I setup a global connection to use in the whole application?
If not, is it good if I open a new connection when request arrives, and close it when handled the request? Is it expensive to open and close a connection?
Should I use a global connection pool? I hear the driver has a native connection pool. Is it a good choice?
If I use a connection pool, how many connections should be used?
Are there other things I should notice?

The primary committer to node-mongodb-native says:
You open do MongoClient.connect once when your app boots up and reuse
the db object. It's not a singleton connection pool each .connect
creates a new connection pool.
So, to answer your question directly, reuse the db object that results from MongoClient.connect(). This gives you pooling, and will provide a noticeable speed increase as compared with opening/closing connections on each db action.

Open a new connection when the Node.js application starts, and reuse the existing db connection object:
/server.js
import express from 'express';
import Promise from 'bluebird';
import logger from 'winston';
import { MongoClient } from 'mongodb';
import config from './config';
import usersRestApi from './api/users';
const app = express();
app.use('/api/users', usersRestApi);
app.get('/', (req, res) => {
res.send('Hello World');
});
// Create a MongoDB connection pool and start the application
// after the database connection is ready
MongoClient.connect(config.database.url, { promiseLibrary: Promise }, (err, db) => {
if (err) {
logger.warn(`Failed to connect to the database. ${err.stack}`);
}
app.locals.db = db;
app.listen(config.port, () => {
logger.info(`Node.js app is listening at http://localhost:${config.port}`);
});
});
/api/users.js
import { Router } from 'express';
import { ObjectID } from 'mongodb';
const router = new Router();
router.get('/:id', async (req, res, next) => {
try {
const db = req.app.locals.db;
const id = new ObjectID(req.params.id);
const user = await db.collection('user').findOne({ _id: id }, {
email: 1,
firstName: 1,
lastName: 1
});
if (user) {
user.id = req.params.id;
res.send(user);
} else {
res.sendStatus(404);
}
} catch (err) {
next(err);
}
});
export default router;
Source: How to Open Database Connections in a Node.js/Express App

Here is some code that will manage your MongoDB connections.
var MongoClient = require('mongodb').MongoClient;
var url = require("../config.json")["MongoDBURL"]
var option = {
db:{
numberOfRetries : 5
},
server: {
auto_reconnect: true,
poolSize : 40,
socketOptions: {
connectTimeoutMS: 500
}
},
replSet: {},
mongos: {}
};
function MongoPool(){}
var p_db;
function initPool(cb){
MongoClient.connect(url, option, function(err, db) {
if (err) throw err;
p_db = db;
if(cb && typeof(cb) == 'function')
cb(p_db);
});
return MongoPool;
}
MongoPool.initPool = initPool;
function getInstance(cb){
if(!p_db){
initPool(cb)
}
else{
if(cb && typeof(cb) == 'function')
cb(p_db);
}
}
MongoPool.getInstance = getInstance;
module.exports = MongoPool;
When you start the server, call initPool
require("mongo-pool").initPool();
Then in any other module you can do the following:
var MongoPool = require("mongo-pool");
MongoPool.getInstance(function (db){
// Query your MongoDB database.
});
This is based on MongoDB documentation. Take a look at it.

Manage mongo connection pools in a single self contained module. This approach provides two benefits. Firstly it keeps your code modular and easier to test. Secondly your not forced to mix your database connection up in your request object which is NOT the place for a database connection object. (Given the nature of JavaScript I would consider it highly dangerous to mix in anything to an object constructed by library code). So with that you only need to Consider a module that exports two methods. connect = () => Promise and get = () => dbConnectionObject.
With such a module you can firstly connect to the database
// runs in boot.js or what ever file your application starts with
const db = require('./myAwesomeDbModule');
db.connect()
.then(() => console.log('database connected'))
.then(() => bootMyApplication())
.catch((e) => {
console.error(e);
// Always hard exit on a database connection error
process.exit(1);
});
When in flight your app can simply call get() when it needs a DB connection.
const db = require('./myAwesomeDbModule');
db.get().find(...)... // I have excluded code here to keep the example simple
If you set up your db module in the same way as the following not only will you have a way to ensure that your application will not boot unless you have a database connection you also have a global way of accessing your database connection pool that will error if you have not got a connection.
// myAwesomeDbModule.js
let connection = null;
module.exports.connect = () => new Promise((resolve, reject) => {
MongoClient.connect(url, option, function(err, db) {
if (err) { reject(err); return; };
resolve(db);
connection = db;
});
});
module.exports.get = () => {
if(!connection) {
throw new Error('Call connect first!');
}
return connection;
}

If you have Express.js, you can use express-mongo-db for caching and sharing the MongoDB connection between requests without a pool (since the accepted answer says it is the right way to share the connection).
If not - you can look at its source code and use it in another framework.

You should create a connection as service then reuse it when need.
// db.service.js
import { MongoClient } from "mongodb";
import database from "../config/database";
const dbService = {
db: undefined,
connect: callback => {
MongoClient.connect(database.uri, function(err, data) {
if (err) {
MongoClient.close();
callback(err);
}
dbService.db = data;
console.log("Connected to database");
callback(null);
});
}
};
export default dbService;
my App.js sample
// App Start
dbService.connect(err => {
if (err) {
console.log("Error: ", err);
process.exit(1);
}
server.listen(config.port, () => {
console.log(`Api runnning at ${config.port}`);
});
});
and use it wherever you want with
import dbService from "db.service.js"
const db = dbService.db

I have been using generic-pool with redis connections in my app - I highly recommend it. Its generic and I definitely know it works with mysql so I don't think you'll have any problems with it and mongo
https://github.com/coopernurse/node-pool

I have implemented below code in my project to implement connection pooling in my code so it will create a minimum connection in my project and reuse available connection
/* Mongo.js*/
var MongoClient = require('mongodb').MongoClient;
var url = "mongodb://localhost:27017/yourdatabasename";
var assert = require('assert');
var connection=[];
// Create the database connection
establishConnection = function(callback){
MongoClient.connect(url, { poolSize: 10 },function(err, db) {
assert.equal(null, err);
connection = db
if(typeof callback === 'function' && callback())
callback(connection)
}
)
}
function getconnection(){
return connection
}
module.exports = {
establishConnection:establishConnection,
getconnection:getconnection
}
/*app.js*/
// establish one connection with all other routes will use.
var db = require('./routes/mongo')
db.establishConnection();
//you can also call with callback if you wanna create any collection at starting
/*
db.establishConnection(function(conn){
conn.createCollection("collectionName", function(err, res) {
if (err) throw err;
console.log("Collection created!");
});
};
*/
// anyother route.js
var db = require('./mongo')
router.get('/', function(req, res, next) {
var connection = db.getconnection()
res.send("Hello");
});

If using express there is another more straightforward method, which is to utilise Express's built in feature to share data between routes and modules within your app. There is an object called app.locals. We can attach properties to it and access it from inside our routes. To use it, instantiate your mongo connection in your app.js file.
var app = express();
MongoClient.connect('mongodb://localhost:27017/')
.then(client =>{
const db = client.db('your-db');
const collection = db.collection('your-collection');
app.locals.collection = collection;
});
// view engine setup
app.set('views', path.join(__dirname, 'views'));
This database connection, or indeed any other data you wish to share around the modules of you app can now be accessed within your routes with req.app.locals as below without the need for creating and requiring additional modules.
app.get('/', (req, res) => {
const collection = req.app.locals.collection;
collection.find({}).toArray()
.then(response => res.status(200).json(response))
.catch(error => console.error(error));
});
This method ensures that you have a database connection open for the duration of your app unless you choose to close it at any time. It's easily accessible with req.app.locals.your-collection and doesn't require creation of any additional modules.

Best approach to implement connection pooling is you should create one global array variable which hold db name with connection object returned by MongoClient and then reuse that connection whenever you need to contact Database.
In your Server.js define var global.dbconnections = [];
Create a Service naming connectionService.js. It will have 2 methods getConnection and createConnection.
So when user will call getConnection(), it will find detail in global connection variable and return connection details if already exists else it will call createConnection() and return connection Details.
Call this service using <db_name> and it will return connection object if it already have else it will create new connection and return it to you.
Hope it helps :)
Here is the connectionService.js code:
var mongo = require('mongoskin');
var mongodb = require('mongodb');
var Q = require('q');
var service = {};
service.getConnection = getConnection ;
module.exports = service;
function getConnection(appDB){
var deferred = Q.defer();
var connectionDetails=global.dbconnections.find(item=>item.appDB==appDB)
if(connectionDetails){deferred.resolve(connectionDetails.connection);
}else{createConnection(appDB).then(function(connectionDetails){
deferred.resolve(connectionDetails);})
}
return deferred.promise;
}
function createConnection(appDB){
var deferred = Q.defer();
mongodb.MongoClient.connect(connectionServer + appDB, (err,database)=>
{
if(err) deferred.reject(err.name + ': ' + err.message);
global.dbconnections.push({appDB: appDB, connection: database});
deferred.resolve(database);
})
return deferred.promise;
}

In case anyone wants something that works in 2021 with Typescript, here's what I'm using:
import { MongoClient, Collection } from "mongodb";
const FILE_DB_HOST = process.env.FILE_DB_HOST as string;
const FILE_DB_DATABASE = process.env.FILE_DB_DATABASE as string;
const FILES_COLLECTION = process.env.FILES_COLLECTION as string;
if (!FILE_DB_HOST || !FILE_DB_DATABASE || !FILES_COLLECTION) {
throw "Missing FILE_DB_HOST, FILE_DB_DATABASE, or FILES_COLLECTION environment variables.";
}
const client = new MongoClient(FILE_DB_HOST, {
useNewUrlParser: true,
useUnifiedTopology: true,
});
class Mongoose {
static FilesCollection: Collection;
static async init() {
const connection = await client.connect();
const FileDB = connection.db(FILE_DB_DATABASE);
Mongoose.FilesCollection = FileDB.collection(FILES_COLLECTION);
}
}
Mongoose.init();
export default Mongoose;
I believe if a request occurs too soon (before Mongo.init() has time to finish), an error will be thrown, since Mongoose.FilesCollection will be undefined.
import { Request, Response, NextFunction } from "express";
import Mongoose from "../../mongoose";
export default async function GetFile(req: Request, res: Response, next: NextFunction) {
const files = Mongoose.FilesCollection;
const file = await files.findOne({ fileName: "hello" });
res.send(file);
}
For example, if you call files.findOne({ ... }) and Mongoose.FilesCollection is undefined, then you will get an error.

npm i express mongoose
mongodb.js
const express = require('express');
const mongoose =require('mongoose')
const app = express();
mongoose.set('strictQuery', true);
mongoose.connect('mongodb://localhost:27017/db_name', {
useNewUrlParser: true,
useUnifiedTopology: true
})
.then(() => console.log('MongoDB Connected...'))
.catch((err) => console.log(err))
app.listen(3000,()=>{ console.log("Started on port 3000 !!!") })
node mongodb.js

Using below method you can easily manage as many as possible connection
var mongoose = require('mongoose');
//Set up default mongoose connection
const bankDB = ()=>{
return mongoose.createConnection('mongodb+srv://<username>:<passwprd>#mydemo.jk4nr.mongodb.net/<database>?retryWrites=true&w=majority',options);
}
bankDB().then(()=>console.log('Connected to mongoDB-Atlas bankApp...'))
.catch((err)=>console.error('Could not connected to mongoDB',err));
//Set up second mongoose connection
const myDB = ()=>{
return mongoose.createConnection('mongodb+srv://<username>:<password>#mydemo.jk4nr.mongodb.net/<database>?retryWrites=true&w=majority',options);
}
myDB().then(()=>console.log('Connected to mongoDB-Atlas connection 2...'))
.catch((err)=>console.error('Could not connected to mongoDB',err));
module.exports = { bankDB(), myDB() };

How to use another MongoDB database using Node.js [duplicate]

How do I connect to mongodb with node.js?
I have the node-mongodb-native driver.
There's apparently 0 documentation.
Is it something like this?
var mongo = require('mongodb/lib/mongodb');
var Db= new mongo.Db( dbname, new mongo.Server( 'mongolab.com', 27017, {}), {});
Where do I put the username and the password?
Also how do I insert something?
Thanks.

Per the source:
After connecting:
Db.authenticate(user, password, function(err, res) {
// callback
});

Everyone should use this source link:
http://mongodb.github.com/node-mongodb-native/contents.html
Answer to the question:
var Db = require('mongodb').Db,
MongoClient = require('mongodb').MongoClient,
Server = require('mongodb').Server,
ReplSetServers = require('mongodb').ReplSetServers,
ObjectID = require('mongodb').ObjectID,
Binary = require('mongodb').Binary,
GridStore = require('mongodb').GridStore,
Code = require('mongodb').Code,
BSON = require('mongodb').pure().BSON,
assert = require('assert');
var db = new Db('integration_tests', new Server("127.0.0.1", 27017,
{auto_reconnect: false, poolSize: 4}), {w:0, native_parser: false});
// Establish connection to db
db.open(function(err, db) {
assert.equal(null, err);
// Add a user to the database
db.addUser('user', 'name', function(err, result) {
assert.equal(null, err);
// Authenticate
db.authenticate('user', 'name', function(err, result) {
assert.equal(true, result);
db.close();
});
});
});

var mongo = require('mongodb');
var MongoClient = mongo.MongoClient;
MongoClient.connect('mongodb://'+DATABASEUSERNAME+':'+DATABASEPASSWORD+'#'+DATABASEHOST+':'DATABASEPORT+'/'+DATABASENAME,function(err, db){
if(err)
console.log(err);
else
{
console.log('Mongo Conn....');
}
});
//for local server
//in local server DBPASSWOAD and DBusername not required
MongoClient.connect('mongodb://'+DATABASEHOST+':'+DATABASEPORT+'/'+DATABASENAME,function(err, db){
if(err)
console.log(err);
else
{
console.log('Mongo Conn....');
}
});

I find using a Mongo url handy. I store the URL in an environment variable and use that to configure servers whilst the development version uses a default url with no password.
The URL has the form:
export MONGODB_DATABASE_URL=mongodb://USERNAME:PASSWORD#DBHOST:DBPORT/DBNAME
Code to connect this way:
var DATABASE_URL = process.env.MONGODB_DATABASE_URL || mongodb.DEFAULT_URL;
mongo_connect(DATABASE_URL, mongodb_server_options,
function(err, db) {
if(db && !err) {
console.log("connected to mongodb" + " " + lobby_db);
}
else if(err) {
console.log("NOT connected to mongodb " + err + " " + lobby_db);
}
});

My version:
var MongoClient = require('mongodb').MongoClient;
MongoClient.connect('mongodb://user:pass#dhost:port/baseName', function(err, db) {
if (err) {
console.error(err);
}
var collection = db.collection('collectionName');
collection.find().toArray(function(err, docs) {
console.log(docs);
});
});

I recommend mongoskin I just created.
var mongo = require('mongoskin');
var db = mongo.db('admin:pass#localhost/mydb?auto_reconnnect');
db.collection('mycollection').find().toArray(function(err, items){
// do something with items
});
Is mongoskin sync? Nop, it is async.

Here is new may to authenticate from "admin" and then switch to your desired DB for further operations:
var MongoClient = require('mongodb').MongoClient;
var Db = require('mongodb').Db, Server = require('mongodb').Server ,
assert = require('assert');
var user = 'user';
var password = 'password';
MongoClient.connect('mongodb://'+user+':'+password+'#localhost:27017/opsdb',{native_parser:true, authSource:'admin'}, function(err,db){
if(err){
console.log("Auth Failed");
return;
}
console.log("Connected");
db.collection("cols").find({loc:{ $eq: null } }, function(err, docs) {
docs.each(function(err, doc) {
if(doc) {
console.log(doc['_id']);
}
});
});
db.close();
});

This worked for me:
Db.admin().authenticate(user, password, function() {} );

You can do it like this
var db = require('mongo-lite').connect('mongodb://localhost/test')
more details ...

if you continue to have problems with the native driver, you can also check out sleepy mongoose. It's a python REST server that you can simply access with node request to get to your Mongo instance.
http://www.snailinaturtleneck.com/blog/2010/02/22/sleepy-mongoose-a-mongodb-rest-interface/

With the link provided by #mattdlockyer as reference, this worked for me:
var mongo = require('mongodb');
var server = new mongo.Server(host, port, options);
db = new mongo.Db(mydb, server, {fsync:true});
db.open(function(err, db) {
if(!err) {
console.log("Connected to database");
db.authenticate(user, password, function(err, res) {
if(!err) {
console.log("Authenticated");
} else {
console.log("Error in authentication.");
console.log(err);
}
});
} else {
console.log("Error in open().");
console.log(err);
};
});
exports.testMongo = function(req, res){
db.collection( mycollection, function(err, collection) {
collection.find().toArray(function(err, items) {
res.send(items);
});
});
};

Slight typo with Chris' answer.
Db.authenticate(user, password, function({ // callback }));
should be
Db.authenticate(user, password, function(){ // callback } );
Also depending on your mongodb configuration, you may need to connect to admin and auth there first before going to a different database. This will be the case if you don't add a user to the database you're trying to access. Then you can auth via admin and then switch db and then read or write at will.

const { MongoClient } = require('mongodb');
// or as an es module:
// import { MongoClient } from 'mongodb'
// Connection URL
const url = 'mongodb://localhost:27017';
const client = new MongoClient(url);
// Database Name
const dbName = 'myProject';
async function main() {
// Use connect method to connect to the server
await client.connect();
console.log('Connected successfully to server');
const db = client.db(dbName);
const collection = db.collection('documents');
// the following code examples can be pasted here...
return 'done.';
}
main()
//what to do next
.then(console.log)
//if there is an error
.catch(console.error)
// what to do in the end(function result won't matter here, it will execute always).
.finally(() => client.close());
you can find more in the documentation here: https://mongodb.github.io/node-mongodb-native/4.1/

I'm using Mongoose to connect to mongodb.
Install mongoose npm using following command
npm install mongoose
var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost:27017/database_name', function(err){
if(err){
console.log('database not connected');
}
});
var Schema = mongoose.Schema;
var userschema = new Schema ({});
var user = mongoose.model('collection_name', userschema);
we can use the queries like this
user.find({},function(err,data){
if(err){
console.log(err);
}
console.log(data);
});

how to write a script file which can run multiple nodejs program

I have few java script files which will push some initial configuration data to the database one of the sample file is shown below
var mongoose = require('mongoose'),
config = require('../../config/config');
var PassportLocalUser = require('../models/Passport_LocalUsers');
Schema = mongoose.Schema;
mongoose.connect(config.db);
PassportLocalUser.findOneAndRemove({"username": 'admin'}, function(err){
if(err) {
console.log(err)
}else{
console.log("removed previous admin document ")
PassportLocalUser.findOneAndRemove({"username": 'user'}, function(err){
if(err) {
console.log(err)
}else{
console.log("removed previous admin document ")
generateUserCredentials();
}
});
}
});
function generateUserCredentials(){
var userObj = new PassportLocalUser();
userObj.username="admxcvin";
userObj.password="$2a$10$7/xcvxcvxcvzyPNb1XxbAKG2INj4/R.TYrn0a.k9jrLvrifiV/V6RDxhpTaht6";
userObj.save(function(err,result){
generatePublicUserCredentials();
if(err)
console.log(err)
console.log("Credencials generated")
})
};
function generatePublicUserCredentials(){
var userObj = new PassportLocalUser();
userObj.username="user";
userObj.password="$2a$10$JzLQmIThoU4swr36KUmcAO5QK5.J529qW5saO36jzgShKJV/EfBsi";
userObj.email="user#gmail.com";
userObj.firstName="user";
userObj.lastName="user";
userObj.save(function(err,result){
if(err)
console.log(err)
console.log("Credencials generated")
})
}
now in order to save the data by these multiple files
I type explicitly has node fileName.js Which will generate the data
But now looking for a script which will help me to run all generators at one shot.
ie, if a folder name generator has few file like settingsConfigurationGenerator.js, user.js ..........
all these files should run or execute using single script file please provide some pointers to accomplish it.

Node.js: how to load modules without executing them?

I have a simple file model.js like follows:
var mongo = require('mongodb');
var mongoUri = process.env.MONGOLAB_URI ||
process.env.MONGOHQ_URL ||
'mongodb://localhost/mydb';
exports.connect = mongo.Db.connect(mongoUri, function(err, db) {
console.log("Connect to the database successfully")
});
and in my web.js I load the model using model = require('./model.js'). One werid thing is that although I did not call model.connect(), the message "Connect to the database successfully" still got logged to my console. Why is this happening and is there a way to avoid it?
EDIT:Never mind I have found a workaround:
exports.connect = function(){
mongo.Db.connect(mongoUri, function(err, db) {
console.log("Connect to the database successfully")
});
}

exports.connect = mongo.Db.connect(mongoUri, function(err, db) {
console.log("Connect to the database successfully")
});
You just called mongo.Db.connect() and assigned its result to exports.connect.
That code runs as soon as you require() the module.
Instead, you need to create a function:
exports.connect = function() { ... };