如何在Node JS中的不同文件之间共享一个数据库连接？

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?

Answer 1

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.