mongodb.js

//Importing mongodb and mongoose modules
var mongodb = require('mongodb');
var mongoose = require("mongoose");
//var url = 'mongodb://localhost:27017/urlShortener';
//var url = 'mongodb://theokeles:Ckdnsdacd#050@ds145669.mlab.com:45669/mongolad';
//Protecting the credentials by setting env variables in Heroku, not exposing in public repo
var url = process.env.MONGOLAB_URI;
//Using global promise since mongoose promise is deprecated
mongoose.Promise = global.Promise;

console.log("Mongoose stuff");

//Making mongodb connection from mongoose ODM
var dbconn = mongoose.connect(url, function(error) {
    if (error) {
        return console.log("Error in connecting to mongodb ", error);
    } else {
        console.log("Connection successful to mongo db on local");
    }
});

//Create a Schema(object) -- a predefined structure/format for the documents in the 'urlshortener' collection.
//Schema are the blueprint(class) for the documents in the collection.
var urlShortnerSchema = mongoose.Schema({
    originalLongUrl: String,
    urlCode: {
        type: Number,
        index: true
    },
    shortURL: String
});

//Counters collection keeps track of the latest count_sequences of different fields
//Schema for counters collection
var countersCollectionSchema = mongoose.Schema({
    "_id": String,
    "sequence_value": Number
});

//Models are constructors compiled from Schema definitions.
//Creating a model(object) for querying,creating and validating documents in 'UrlData' collection based on the specific schema(urlShortnerSchema).
var urlShortenerModel = dbconn.model('urldata', urlShortnerSchema);
//Model for counter collection
var countersCollectionModel = dbconn.model('counter', countersCollectionSchema);

//One time create&insert (initialize) counter collection with - sequence_value": 1000
//Code run on the time of require('mongodb.js') load

//Below code snippet must go inside callback else it is initilising everytime check??????
var counterData = {
    "_id": "urlCode",
    "sequence_value": 1000
};
var counterEntry = new countersCollectionModel(counterData);
//Promise returned on adding new counter doc
var counterPromise = counterEntry.save();

//Search if any document exists ????? count()? maybe
countersCollectionModel.find({ "sequence_value": 1000 }, function(error, docs) {
    if (error) {
        console.log("An error has occured", error);
    } else {
        if (docs.length === 0) {
            counterPromise.then(function(docs) {
                console.log("Initial counter doc with sequence_value " + docs + " saved to db");
            });
        }
    }
});

//module.exports object contains those contents(functions and data) that we want other files to use
module.exports = {
    //Check validity of short URL and redirect
    checkIfShortUrlExist: function(shortUrl) {
        var checkPromise = urlShortenerModel.findOne({ 'shortURL': shortUrl }).exec();
        return checkPromise;
    },
    //Retrieve the next urlCode sequence value 
    getLatestUrlCodeSequence: function(sequenceName) {
        //query({}).exec() returns a js Promise(mongoose default)
        var counterPromise = countersCollectionModel.find({ _id: sequenceName }).exec();
        /*counterPromise.then(function(sequence_doc) {
                console.log("docs", sequence_doc);
                return sequence_doc;
            })
            .then(function(sequence_doc) {
                console.log('sequence_doc.sequence_value', sequence_doc.sequence_value);
                sequence_doc.sequence_value = sequence_doc.sequence_value + 1;
                urlCode = sequence_doc.sequence_value;
                return sequence_doc.save();
            })
            .then(function(docs) {
                console.log("The doc " + docs + " is saved");
                return urlCode;
            });*/
        return counterPromise;
    },

    //Increment (Update) the counters collection sequenceField
    incrementCounter: function() {
        //Use update() to modify document in mongoose instead of save()
        //~update({find query},{modify data query},options,callback)~
        //update().exec() returns Promise
        var counterUpdatePromise = countersCollectionModel.update({ "_id": "urlCode" }, { $inc: { sequence_value: 1 } }).exec();
        return counterUpdatePromise;
    },

    //Save new documents(urlData) to collection 
    enterNewUrlData: function(newUrlData) {
        //New instance of model to enter new document
        var newEntry = new urlShortenerModel(newUrlData);
        //Document entry into db
        /*newEntry.save(function(error) {
            if (error) {
                return console.log("An error has occured: ", error);
            } else {
                console.log("Entry saved to collection in db");
            }
        });*/
        //Mongoose save() function returns promise
        var savePromise = newEntry.save();
        return savePromise;
    },

    //Check for duplicate URL in db
    checkDuplicateData: function(inputUrl) {
            //console.log("Inside checkDuplicateData");
            var isDuplicateUrl;
            var query = urlShortenerModel.find({ 'originalLongUrl': inputUrl });
            var queryPromise = query.exec();
            /*promise.then(function(doc) {
                console.log("Inside promise then()");
                isDuplicateUrl = true;
                if (doc.length == 0) {
                    isDuplicateUrl = false;
                } else {
                    isDuplicateUrl = true;
                }
                console.log("--isDuplicateUrl-- ", isDuplicateUrl);
            });
            return isDuplicateUrl;*/
            return queryPromise;
        }
        /*checkDuplicateData: function(inputUrl) {
            urlShortenerModel.find({
                'originalLongUrl': inputUrl
            }, function(error, docs) {
                if (error) {
                    return console.log('An error has occured', error);
                } else {
                    console.log("Queried docs ", docs);
                    console.log("docs.length	: ", docs.length);
                    if (docs.length !== 0) {
                        var isDuplicate = true;
                        console.log("There is a duplicate url in the db");
                    } else {
                        console.log('Valid url for entry to db');
                        var newUrlData = {
                            originalLongUrl: inputUrl,
                            urlCode: 0
                        };
                        var newEntry = new urlShortenerModel(newUrlData);
                        //Document entry into db
                        newEntry.save(function(error) {
                            if (error) {
                                return console.log("An error has occured: ", error);
                            } else {
                                console.log("Entry saved to collection in db");
                            }
                        });
                    }
                }
            });
        }*/
};

//Model is used for querying,creating,retrieving documents.
//On enetring a document not following the Schema, a validation error will be thrown