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Open Multiple MongoDB connection in Express.js App

ziishaned profile image Zeeshan Ahmd ・2 min read

This tutorial aims to show you how to open multiple MongoDB connections in Express.js application.

Now we want to create a package.json file which will keep track of our dependencies information. To do that create a new file and put following content inside of it:

{
  "name": "mongo-conn",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "scripts": {
    "seed": "node seeder.js",
    "dev": "nodemon index.js"
  },
  "dependencies": {
    "express": "^4.17.1",
    "faker": "^4.1.0",
    "mongoose": "^5.9.7",
    "nodemon": "^2.0.2"
  }
}
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Let's create a new file and call it index.js. This file will holds our main server code. Put the following content inside index.js file:

const express = require('express');
const {userModel, todoModel} = require('./models');
const app = express();

app.get('/users', async (req, res) => {
    const users = await userModel.find({});

    res.json(users);
});

app.get('/todos', async (req, res) => {
    const todos = await todoModel.find({});

    res.json(todos);
});

const port = 3000;
app.listen(port, () => console.log(`App listening at http://localhost:${port}`));
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Now we will create a new file and call it connections.js and put following content inside of it:

const mongoose = require('mongoose');

function makeNewConnection(uri) {
    const db = mongoose.createConnection(uri, {
        useNewUrlParser: true,
        useUnifiedTopology: true,
    });

    db.on('error', function (error) {
        console.log(`MongoDB :: connection ${this.name} ${JSON.stringify(error)}`);
        db.close().catch(() => console.log(`MongoDB :: failed to close connection ${this.name}`));
    });

    db.on('connected', function () {
        mongoose.set('debug', function (col, method, query, doc) {
            console.log(`MongoDB :: ${this.conn.name} ${col}.${method}(${JSON.stringify(query)},${JSON.stringify(doc)})`);
        });
        console.log(`MongoDB :: connected ${this.name}`);
    });

    db.on('disconnected', function () {
        console.log(`MongoDB :: disconnected ${this.name}`);
    });

    return db;
}

const userConnection = makeNewConnection('mongodb://127.0.0.1:27017/user');
const todoConnection = makeNewConnection('mongodb://127.0.0.1:27017/todo');

module.exports = {
    userConnection,
    todoConnection,
};
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Now lets create another file and call it models.js and put following content inside of it:

const mongoose = require('mongoose');
const {userConnection, todoConnection} = require('./connections');

const userSchema = new mongoose.Schema({
    name: String,
    isActive: Boolean,
}, {
    versionKey: false,
    timestamps: true,
});

const todoSchema = new mongoose.Schema({
    title: String,
    completed: Boolean,
}, {
    versionKey: false,
    timestamps: true,
});

const userModel = userConnection.model('User', userSchema);
const todoModel = todoConnection.model('Todo', todoSchema);

module.exports = {
    userModel,
    todoModel,
};
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Now lets create another file and name it seeder.js and put following content inside of it:

const faker = require('faker');

const {userModel, todoModel} = require('./models');
const {userConnection, todoConnection} = require('./connections');

async function seed() {
    for (let i = 0; i< 10; i++) {
        await userModel.create({
            name: faker.name.findName(),
            isActive: faker.random.boolean(),
        });
    }

    for (let i = 0; i < 10; i++) {
        await todoModel.create({
            title: faker.lorem.words(3),
            completed: faker.random.boolean(),
        });
    }
}

seed().then(() => {
    userConnection.close();
    todoConnection.close();
});
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Now open your terminal and seed your database with following command:

yarn seed
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Lets start the application by running following command inside your terminal:

yarn dev
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Now open the following link inside your browser:

http://localhost:3000/users
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You can find the complete source code for this application on my GitHub profile:

Discussion (8)

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janguianof profile image
Jaime Anguiano

Nice!
Is there anyway await the multiple DB connections before the server start listen http traffic? I never had founded a nice way to do that : (

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ziishaned profile image
Zeeshan Ahmd Author • Edited

To do that you have to import the file which contains the MongoDB connection code into main server file. Please have a look at the following code:

Put following code inside connection.js file:

const db = mongoose.createConnection('mongodb://127.0.0.1:27017/user', {
    useNewUrlParser: true,
    useUnifiedTopology: true,
});

db.on('error', function (error) {
    console.log(`MongoDB :: connection ${this.name} ${JSON.stringify(error)}`);
    db.close().catch(() => console.log(`MongoDB :: failed to close connection ${this.name}`));
});

db.on('connected', function () {
    mongoose.set('debug', function (col, method, query, doc) {
        console.log(`MongoDB :: ${this.conn.name} ${col}.${method}(${JSON.stringify(query)},${JSON.stringify(doc)})`);
    });
    console.log(`MongoDB :: connected ${this.name}`);
});

db.on('disconnected', function () {
    console.log(`MongoDB :: disconnected ${this.name}`);
});

module.exports = db;

Now create another file and call it index.js and put following code inside of it:

const express = require('express');
require('./connection');

const app = express();

const port = 3000;
app.listen(port, () => console.log(`App listening at http://localhost:${port}`));
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janguianof profile image
Jaime Anguiano

Thanks for your quick reply! I will try your suggestion

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vigneshncc profile image
Vignesh Gopalakrishnan

Hi, I am working with node + typescript. This approach doesn't seems to work with ts environment.

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ziishaned profile image
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vigneshncc profile image
Vignesh Gopalakrishnan

Hello Zeeshan, Thanks for your code snippet. I took yours as a reference and I ended up changing it accordingly which suits for typescript. I made it very simple for now to work and that is why I haven't added the types fully.

The below code block works fine, except the commented one. All 'this' inside the functions are throwing error and would be great if you help me where I am doing wrong.

import mongoose from "mongoose";
import logger from "./logger";

const makeNewConnection = (uri: string): mongoose.Connection => {
  let conn: mongoose.Connection = mongoose.createConnection(uri, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
    useCreateIndex: true,
  });

  /* conn.on("error", function (error) {
    logger.info(`MongoDB :: connection ${this.name} ${JSON.stringify(error)}`);
    conn
      .close()
      .catch(() =>
        logger.warn(`MongoDB :: failed to close connection ${this.name}`)
      );
  });

  conn.on("connected", function () {
    mongoose.set("debug", function (col, method, query, doc) {
      logger.debug(
        `MongoDB :: ${this.conn.name} ${col}.${method}(${JSON.stringify(
          query
        )},${JSON.stringify(doc)})`
      );
    });
    logger.info(`MongoDB :: connected ${this.name}`);
  });

  conn.on("disconnected", function () {
    logger.info(`MongoDB :: disconnected ${this.name}`);
  }); */

  return conn;
};

const dbOne= makeNewConnection(process.env.DB_ONE);
const dbTwo = makeNewConnection(process.env.DB_TWO);

export { dbOne, dbTwo };
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Thread Thread
piotrmonsiorski profile image
Piotr Monsiorski

It's quite old question, but this may help someone in the future: check if your process.env variables aren't undefined. To fix this, you can move dotenv.config(); to connections.js file and use in before makeNewConnection(...) function.

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ho3einmolavi profile image
Hossein Molavi

amazing
the best solution

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