Question

I’m developing a express.js application, without mongoose.

What I’m trying to do is, to encapsulate calls to mongodb inside a function, pass the function some parameter and get the data back from mongodb.

The problem I’m running into is explained by the code below

function get_data()
{
    var mongo = require('mongodb'),Server = mongo.Server,Db = mongo.Db;
    var server = new Server('localhost', 27017, {auto_reconnect: true});
    var db = new Db('test', server); 

    db.collection('test_collection', function(err, collection) {

        collection.find().toArray(function(err, items) {
            var data = items;
        });
    });

    console.log(data);
    console.log("in get");
    return data;
}

How do I return the items Array I pulled from mongo db from this function.

I want to know how scoping works in javascript and how do I put the items in a variable and return them from the get_data function.

After the answer

I fixed the code. It now works and looks like this.

function get_data(callback) { 
    var mongo = require('mongodb'),Server = mongo.Server,Db = mongo.Db;
    var server = new Server('localhost', 27017, {auto_reconnect: true});
    var db = new Db('test', server);

    db.open(function(err, db) {
        if (err) return callback(err);

        db.collection('test_collection', function(err, collection) {
            if (err) return callback(err);
            collection.find().toArray(callback);
        });
    });
}


get_data(function(err, items) {
    // handle error
    console.log(items);
});

Answer 1

Since the items are retrieved from MongoDB asynchronously, the function get_data needs to accept a callback that will be used to return the results. I believe you’ll also need to explicitly open the database connection.

function get_data(callback) {
    ...

    db.open(function(err, db) {
        if (err) return callback(err);

        db.collection('test_collection', function(err, collection) {
            if (err) return callback(err);
            collection.find().toArray(callback);
        });
    });
}

get_data(function(err, items) {
    // handle error
    console.log(items);
});