Moving nodejs MongoDB connection code to another file

Question

Moving the database connection code another nodejs file, no connection object is returned.

I can write data to MongoDB in nodejs. All db connection code is written in a single .js file.

Now I try to seperate the db connection code to another .js file, and now it seems that no connection can be made successfully.

Here is the working code in 1 .js file:

  const mongoDBIP = '192.168.1.71';
  const mongoDBPort = 27017;

  const mongo= require('mongodb').MongoClient;
  const mongoURL = 'mongodb://<mongo admin>:<password>@'+`${mongoDBIP}`+':'+`${mongoDBPort}`;

  ...

    mongo.connect(mongoURL, { useNewUrlParser: true, useUnifiedTopology: true }, (err, db) => {
    if (err) {}

    var dbo = db.db(<databaseName>);

    var collection = dbo.collection('messages');

    collection.insertOne(message, (err, result) => {
            if (err) {}
    })

  ...

Now I break this into 2 .js files:

  var _mongo = require('./mongodb.js');

  var mongoDBO = _mongo.mongoDBO;

  ...

    var dbo = mongoDBO('feathers');

    console.log('DBO:' + dbo);   <-- here, dbo is NULL

    var collection = dbo.collection('messages');

    collection.insertOne(message, (err, result) => {
            if (err) {}
    })

  ...

Here is the content of mongodb.js:

  // mongodb.js

  const mongoDBIP = '192.168.1.71';
  const mongoDBPort = 27017;

  const mongoClient = require('mongodb').MongoClient;
  const mongoURL = 'mongodb://<mongo admin>:<password>@'+`${mongoDBIP}`+':'+`${mongoDBPort}`;


  function mongoDBO(database) {

    var dbo;

    mongoClient.connect(mongoURL, { useNewUrlParser: true, useUnifiedTopology: true }, (err, dbase) => {
            if (err) {}
            dbo = dbase.db(database);   <-- here, dbo is NULL
    });

    return dbo;
  }

  module.exports = Object.freeze({
      mongoDBO
  });

I expect the object "dbo" in mongodb.js would not be NULL, but it is. This occurs under both nodejs v10.x and v12.x.

can you check if (err) { console.log(err); throw err; } to be sure if there is no error to connecting in mongodb.js? — SuleymanSah
– SuleymanSah, Commented Oct 12, 2019 at 14:42

SuleymanSah · Accepted Answer · 2019-10-13 08:13:56Z

2

Here is an implementation what Tom explained, in case you need.

mongodb.js

const mongoClient = require('mongodb').MongoClient;

const mongoDBIP = '192.168.1.71';
const mongoDBPort = 27017;

const mongoURL = 'mongodb://<mongo admin>:<password>@'+`${mongoDBIP}`+':'+`${mongoDBPort}`;

let _db;

const initDb = callback => {
  if (_db) {
    console.log('Db is already initialized!');
    return callback(null, _db);
  }
  mongoClient .connect(mongoURL)
    .then(client => {
      _db = client;
      callback(null, _db);
    })
    .catch(err => {
      callback(err);
    });
};

const getDb = () => {
  if (!_db) {
    throw Error('Db not initialized');
  }
  return _db;
};

module.exports = {
  initDb,
  getDb
};

Initialize it in your main file (index, app or server.js)

const mongodb = require('./mongodb');


mongodb.initDb((err, mongodb ) => {
  if (err) {
    console.log(err);
  } else {
    app.listen(3000);
  }
});

And use it in your routes:

const mongodb = require('./mongodb');


  mongodb.getDb()
    .db()
    .collection('your_collection_name')....

edited Oct 13, 2019 at 8:13

answered Oct 12, 2019 at 15:30

SuleymanSah

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6 Comments

SuleymanSah Over a year ago

@charleslcso I noticed a mistake in my code, edited to answer only this part changed in main file: mongodb.initDb((err, mongodb ) => ... Can you try again with this change?

charleslcso Over a year ago

I get this... initDb error MongoNetworkError: Authentication failed, because of this...UnhandledPromiseRejectionWarning: Error: Db not initialized

SuleymanSah Over a year ago

@charleslcso did you mongoDb.init before listening app? Can you share your main file code (index.js, server.js)

charleslcso Over a year ago

I edited your code to show mine. Basically the same.

SuleymanSah Over a year ago

@charleslcso do you have a github repo for this app so that I can check?

|

Tom Boutell · Accepted Answer · 2019-10-12 15:10:56Z

0

You are trying to return a value that does not exist yet. dbo is not set until the callback function is invoked. The original function has already returned at that point.

You must alter your mongodb.js file to export a function that takes a callback, and passes dbo to that callback when it is ready.

I recommend reading up on callbacks and asynchronous programming.

answered Oct 12, 2019 at 15:10

Tom Boutell

7,6321 gold badge31 silver badges27 bronze badges

Comments

Ankit Kumar Rajpoot · Accepted Answer · 2019-10-12 15:47:18Z

0

Try like this

const mongoDBIP = "192.168.1.71";
const mongoDBPort = 27017;
const mongoClient = require("mongodb").MongoClient;
const mongoURL =
  "mongodb://<mongo admin>:<password>@" +
  `${mongoDBIP}` +
  ":" +
  `${mongoDBPort}`;

var mongoDBO = database =>
  new Promise((resolve, reject) => {
    mongoClient.connect(
      mongoURL,
      { useNewUrlParser: true, useUnifiedTopology: true },
      (err, dbase) => {
        if (err) {
          reject(err);
        }
        resolve(dbase);
      }
    );
  });

module.exports = Object.freeze({
  mongoDBO
});

&

var _mongo = require('./mongodb.js');

var mongoDBO = _mongo.mongoDBO;

...

try {
    let dbo = mongoDBO('feathers');

    console.log('DBO:' + dbo);   <-- here, dbo is NULL

    var collection = dbo.collection('messages');

    collection.insertOne(message, (err, result) => {
            if (err) {}
    })
} catch (error) {
    console.log(connection failed)
}


...

answered Oct 12, 2019 at 15:47

Ankit Kumar Rajpoot

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5 Comments

charleslcso Over a year ago

Thanks for the code. I still have not got the handle of Promise object... but it doesn't work... there should be error in the line dbo.collection.

Ankit Kumar Rajpoot Over a year ago

If you want to insert data after connection the you can use like this. var Fees = require("../../../models/fees");

charleslcso Over a year ago

I edited your code to show mine. Now, DBO is [object Promise]. dbase is : [object Object]. I think both is good. But it shows "connection failed". I think the error is in dbo.collection('messages')

Ankit Kumar Rajpoot Over a year ago

You should use var Fees = require("../../../models/fees") instead of dbo.collection('messages')

David Makogon Over a year ago

@charleslcso - Please do not edit someone's code (it effectively changes the answer and alters the intent of the person answering). You can reply in a comment about the differences.

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