While loop to check uniqueness of custom id - node.js

Question

I have a MongoDB databse set up with some objects that have a unique code (not the primary key).
I should also note that I'm using NodeJS and this code is in my server.js to connect to the MongoDB database.
To generate a new code, I generate one randomly and I want to check if it already exists. If not then we use it no problem, but if it already exists I want to generate another code and check it again. This is the code I use to check if the id already exists:
function createPartyId(callback) {
var min = 10000, max = 99999;
var partyId = -1, count = -1;
async.whilst(
function () { return count != 0; },
function (callback) {
partyId = min + Math.floor(Math.random() * (max - min + 1));
partyId = 88888;
getPartyIdCount(partyId, function(num) {
count = num;
});
},
function (err) {
}
);
}
function getPartyIdCount(partyId, callback) {
count = -1;
db.db_name.find({id: partyId}, function(err, records) {
if(err) {
console.log("There was an error executing the database query.");
callback(count);
}
count = records.length;
callback(count);
});
}

Answer 1

First of all, is there any particular reason you're not using a simple number increment sequence? This type of code is prone to inefficiency, the more numbers you generate the more chance you have of collisions which means you're going to be spending more time on generating an ID for your data than you are on the rest of your processing. Not a good idea.
But I can still tell you what's going wrong.
OK, so getPartyIdCount() will only, ever, always, without fail, return undefined (or, basically, nothing).
Your mongo call processes the return value in a callback, and that callback doesn't assign its value to anything, so return records.length just gets lost into nothingness.
You've mixed up createPartyId(), which it appears you want to run synchronously, with your mongo call, which must run asynchronously.
return always goes with the nearest containing function, so in this case it goes with function(err, records), not function getPartyIdCount(partyId).

Answer 2

(Expanding my comment from above)
The issue is that createPartyId is an asynchronous function, but you're trying to return the value synchronously. That won't work. Once you touch an async operation, the rest of the call stack has to be async as well.
You don't include the code that's calling this, but I assume you want it to be something like:
var partyId = createPartyId();
// do stuff...
That's not going to work. Try this:
function createPartyId(callback) {
var min = 10000, max = 99999;
var partyId = -1, count = -1;
async.whilst(
function () { return (count == 0); },
function (callback) {
partyId = min + Math.floor(Math.random() * (max - min + 1));
partyId = 88888;
getPartyIdCount(partyId, function(err, num) {
if (!err) {
count = num;
}
callback(err);
});
},
function (err) {
// this is called when the loop ends, error or not
// Invoke outer callback to return the result
callback(err, count);
}
);
}
function getPartyIdCount(partyId, callback) {
count = -1;
db.db_name.find({id: partyId}, function(err, records) {
if(err) {
console.log("There was an error executing the database query.");
callback(err);
}
count = records.length;
callback(null, count);
});
}
(I've also adopted the default node.js convention of always returning errors as the first argument to callback functions.)
So, to use this you would do:
getPartyId(function (err, num) {
if (err) { return aughItFellOver(err); }
// do stuff
});