Creating incrementing numbers with mongoDB

Question

We have an order system where every order has an id. For accounting purposes we need a way to generate invoices with incremening numbers. What is the best way to do this without

Answer 1

I did not find any working solution, so I implemented the "optimistic loop" in node.js to get Auto-Incrementing Interger ID fields. Uses the async module to realize the while loop.

// Insert the document to the targetCollection. Use auto-incremented integer IDs instead of UIDs. 
function insertDocument(targetCollection, document, callback) {
    var keepRunning = true;
    var seq = 1;
    // $type 16/18: Integer Values
    var isNumericQuery = {$or : [{"_id" : { $type : 16 }}, {"_id" : { $type : 18 }}]};
    async.whilst(testFunction, mainFunction, afterFinishFunction);
    // Called before each execution of mainFunction(). Works like the stop criteria of a while function.
    function testFunction() { 
        return keepRunning; 
    }
    // Called each time the testFunction() passes. It is passed a function (next) which must be called after it has completed.
    function mainFunction(next) {
        findCursor(targetCollection, findCursorCallback, isNumericQuery, { _id: 1 });
        function findCursorCallback(cursor) {
            cursor.sort( { _id: -1 } ).limit(1);
            cursor.each(cursorEachCallback);
        }
        function cursorEachCallback(err, doc) {
            if (err) console.error("ERROR: " + err);
            if (doc != null) {
                seq = doc._id + 1;
                document._id = seq;
                targetCollection.insert(document, insertCallback);
            }
            if (seq === 1) {
                document._id = 1;
                targetCollection.insert(document, insertCallback);
            }
        }
        function insertCallback(err, result) {
            if (err) {
                console.dir(err);
            }
            else {
                keepRunning = false;
            }
            next();
        }
    }
    // Called once after the testFunction() fails and the loop has ended. 
    function afterFinishFunction(err) {
        callback(err, null);
    }
}

// Call find() with optional query and projection criteria and return the cursor object.
function findCursor(collection, callback, optQueryObject, optProjectionObject) {
    if (optProjectionObject === undefined) {
        optProjectionObject = {};
    }
    var cursor = collection.find(optQueryObject, optProjectionObject);
    callback(cursor);
}

Call with

insertDocument(db.collection(collectionName), documentToSave, function() {if(err) console.error(err);});