How to share one database connection across different files in node js?

Question

I have searched a lot but still wasn't able to find a specific ans. I am trying to do following:

In mongo.js

var client = require('mongodb').MongoClient,
mongodb=null;

module.exports =  {
connect: function(dburl, callback) {
    client.connect(dburl,
        function(err, db){
            mongodb = db;
            if(callback) { callback(); }
        });
},
db: function() {
    return mongodb;
},
close: function() {
    mongodb.close();
 }
};

In server.js

mongodb = require('./mongo');
mongodb.connect('mongodb://localhost:27017/mydb', function() {
 console.log('Connected to MongoDB.');
});

In randomfile.js

 mongodb = require('./mongo');
 mongodb.db()
.collection('mycollection')
.find({someField: 'myquery'}, {}, options)
.toArray(function(err, coll) {
    if (err) { throw err; }
    console.log(coll);
});

When I run server.js a connection is formed but when I run randomfile.js I am not able to get the connection. I encounter following error.

TypeError: Cannot read property 'collection' of undefined

Am I doing something wrong?

Why do you not invoke mongo.connect and pass it the address in randomfile.js? I don't see how you expect to get a reference to your database in randomfile.js. — Louis93
– Louis93, Commented May 25, 2015 at 17:58

bluefog · Accepted Answer · 2015-05-25 18:37:53Z

2

When you do anything after the callback gets over, the connection does not persist. To preserve the connection, use connection pooling.

var db; //global database instance
mongodb.MongoClient.connect(MONGODB_URI, function(err, database) {
  if(err) throw err;

  db = database;  //pool the connection
  coll = db.collection('test');

  app.listen(3000);
  console.log('Listening on port 3000');
});
//No need for further calls to connect(), reuse db
//object. Export to other files if necessary.

More info.

For a larger application, a better solution would be to modularize the connection and use it again across all the files of the app.

edited May 25, 2015 at 18:37

answered May 25, 2015 at 17:59

bluefog

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6 Comments

bhaumik Over a year ago

Thanks bluefog. Ya but if for each interaction I need to open a connection to db then, it will introduce a lot of latancy. My object was to create a single connection per db and share across all apis/interaction. Is there any way to achieve this?

bluefog Over a year ago

@bhaumik Creating a connection to the database is usually not a bottleneck. How do you know that repeated connection will create latency issues? Have you faced any issues?

bhaumik Over a year ago

No i haven't till now but I can see that it takes some milli seconds to form a connection and since I am working on a scalable application, this can affect when there are many requests forming connections to same db. Correct me if I am wrong.

bhaumik Over a year ago

thanks for the link. I had already seen it. Since, my code is purely backend (no use of express js), this type of pooling won't help. I guess I need to use some other language, for this purpose.

bluefog Over a year ago

@bhaumik That does not make much sense to me. Connection pooling can be done on any call of connect. It has nothing to do with express at all.

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