Save MongoDB Document With Concurrent Edit Protection

documentModel.js

var mongoose = require("mongoose");
var ObjectId = mongoose.Schema.Types.ObjectId;

//create schema for a post
var PostSchema = new mongoose.Schema({
	nonce: ObjectId, //this is used for protecting against concurrent edits: http://docs.mongodb.org/ecosystem/use-cases/metadata-and-asset-management/
	name:  String,
	dateCreated: { type: Date, default: Date.now },
	dateLastChanged: { type: Date, default: Date.now },
	postData: mongoose.Schema.Types.Mixed
});

//compile schema to model
exports.PostModel = db.model('post', PostSchema);

postController.js

var postService = require('./postService');

exports.AppendPostText = function(postId, text, callback){
	saveGameByIdWithConcurrencyProtection(postId, function(doc, cb){
		doc.postData.text += text;
		cb(null, data);
	}, 0, function(err, doc){
		callback(err, doc);
	});

};

postService.js

var mongoose = require("mongoose");

var models = require("./documentModel");



/*
This method uses the nonce field in the document to protect against concurrent edits on the post document
 http://docs.mongodb.org/ecosystem/use-cases/metadata-and-asset-management/#create-and-edit-content-nodes
 transformFunction will be given the post doc and should callback the data to update:
 transformFunction(doc, callback)
 */
var savePostByIdWithConcurrencyProtection = function(postId, transformFunction, retries, callback){
	FindPostById(postId, function(err, doc){
		if(err || !doc){
			callback(err || "Unable to find post in savePostByIdWithConcurrencyProtection");
			return;
		}
		transformFunction(doc, function(err, data){
			if(err){
				callback(err);
				return;
			}
			data.nonce = new mongoose.Types.ObjectId;
			//setTimeout(function(){ //setTimeout for testing concurrent edits
			models.PostModel.update({"_id":postId, "nonce":doc.nonce}, data, function(err, numberAffected, raw){
				if(err){
					callback(err);
					return;
				}
				//console.log("savePostByIdWithConcurrencyProtection: ", numberAffected, raw);
				if(!numberAffected && retries < 10){
					//we weren't able to update the doc because someone else modified it first, retry
					console.log("Unable to savePostByIdWithConcurrencyProtection, retrying ", retries);
					//retry with a little delay
					setTimeout(function(){
						savePostByIdWithConcurrencyProtection(postId, transformFunction, (retries + 1), callback);
					}, 20);
				} else if(retries >= 10){
					//there is probably something wrong, just return an error
					callback("Couldn't update document after 10 retries in savePostByIdWithConcurrencyProtection");
				} else {
					FindPostById(postId, callback);
				}
			});
			//}, 5000);
		});
	});

};


var FindPostById = function(id, callback){
	//search for an existing post
	models.PostModel.findOne({"_id":id}, function(err, doc){
		if(err){
			console.error("FindPostById:", err);
		} else if(!doc){
			var msg = "Could Not FindPostById:" + id;
			console.error(msg);
			return callback(msg);
		}
		callback(err, doc);
	});
};