node.js calling query inside module

Question

Being new to Node's way of doing things, I am quite confused about how to do what seems to be a trivial use-case:

for a login page, to verify that the passed login/pwd are accurate, i fire a query
- the query resides in a custom module that is in a separate script.

e.g.

var userName = req.body.username;
var userPwd = crypto.hash(req.body.password);
var user = db.getUser(userName, userPwd);
if (user.id) {
     console.log("valid login entered");
} else {
    console.log("INVALID login entered");
}

the db.getUser fn is in a separate file called "db.js". the code in that file is as follows:

var pg = require("pg");
var conString = "pg://<connection string to PostgreSQL DB>";
var client = new pg.Client(conString);
client.connect();
exports.response = [];

exports.getUser = function(username, password) {

    var query = "SELECT id, first_name, last_name FROM usertable where login = $1 and password = $2";

    var query = client.query({
            text: query,
            values: [username, password]
        });

        query.on("row", function (row) {
           console.log("Returned row from getUser query:" + row.id + " and fname:" + row.first_name + " and lname:" + row.last_name);
            response.push(row);
            return response;
    });

    query.on("end", function (result) {
        client.end();
    });
};

due to the callback mechanism, the code enters the "INVALID login entered" debug stmt before the query is done executing.

I guess my main question is: if i want to keep all the DB query code in a separate include file (as opposed to cluttering up the main controller file with that code), how can i ensure that the DB function finishes running and returns a value to the calling code, before the rest of the code executes?

ino1tn0t · Accepted Answer · 2014-09-03 04:18:29Z

Ok, found the answer (at least, an answer; there might be more ways to do this better).

I changed the calling code from:

var user = db.getUser(userName, userPwd);

to:

 var user = db.getUser(userName, userPwd, function(response) {
            console.log("USER INFO:");
            console.log(response, null, "    ");
        });

and modified the db.getUser function from:

exports.getUser = function(username, password) {

    var query = "SELECT id, first_name, last_name FROM usertable where login = $1 and password = $2";

    var query = client.query({
            text: query,
            values: [username, password]
        });

        query.on("row", function (row) {
           console.log("Returned row from getUser query:" + row.id + " and fname:" + row.first_name + " and lname:" + row.last_name);
            response.push(row);
            return response;
    });

    query.on("end", function (result) {
        client.end();
    });
};

to:

exports.getUser = function(username, password, callback) {

    var query = "SELECT id, first_name, last_name FROM usertable where login = $1 and password = $2";

    var query = client.query({
            text: query,
            values: [username, password]
        });

        query.on("row", function (row) {
           console.log("Returned row from getUser query:" + row.id + " and fname:" + row.first_name + " and lname:" + row.last_name);
            response.push(row);
            return callback(response);
    });

    query.on("end", function (result) {
        client.end();
    });

That did the trick ! : ) . Please do let me know if this approach is acceptable, or whether there's a better way of doing it.

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