Question

I’m trying to query database everytime users input messages, nodejs complains “Cannot call method ‘collection’ of null” Below is the code I think the problem comes from.

var mongo = require('mongodb');

var db = new mongo.Db('chat', new mongo.Server('127.0.0.1', '27017', {native_parser:true}));
//testting querying mongo everytime there is message
socket.on('connection', function(client) {
    client.on('message', function(message) {        
        db.open(function(err, db){
            db.collection('sessions', function(err, collection){
                collection.count(function(err, count) {
                  sys.puts("There are " + count + " records.");
                });
            });
        });
    });
});

note: the first user’s message, I got the sys.puts count right, no errors. but the second input will cause error.

Answer 1

db.open(function(err, db){
    socket.on('connection', function(client) {
        });
    });
});

As Raynos suggested putting db.open in outer of closure will solve the problem.