Mongoose save isn't inserting anything - mysql

Question

var mongoose = require('mongoose');
var url = mongoUrl + dbCollectionName; //external var
var db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function (callback) {
console.log(getTimeStamp() + 'Connected to Mongo with Mongoose');
insertDocuments(db, function () {
});
});
mongoose.connect(url);
// Creating our Schema
var ackSchema = mongoose.Schema({
hostgroup : String,
host : String,
service : String,
timePeriod : String,
startTime : Number,
ackTime : Number,
deltaTime : Number,
caseNumb : String,
state : Number,
author : String,
ackId : Number,
});
// Creation our model
var ackModel = mongoose.model(collectionName, ackSchema);
//////////////////////////////////////
//// Functions
var insertDocuments = function(db, callback) {
// Get the documents collection
var collection = db.collection(collectionName);
var returnValue = 0,
caseValue = "";
// Find item to compare
collection.find({}).toArray( function (err, docs) {
// If Collection does not exist => 0, else 1
if (docs.length === 0) {
colExist = 0;
console.log(getTimeStamp() + 'Collection is empty. If needed application will create "' + collectionName + '" collection while inserting items.');
} else {
colExist = 1;
console.log(getTimeStamp() + 'Collection "' + collectionName + '" exist, item will be added');
};
// SQL Query to fetch row
mysqlQuery(function (row) {
//// IF 8/20
if (row.timeperiod == timePeriod820) {
returnValue = timePeriodCalc(row); // Function from timeperiod.js
deltaValue = parseInt(returnValue.slice(6)); // Get our Delta Value
caseValue = returnValue.slice(0,4); // Get the Case Number, verification purpose
//// ELSE 24/7
} else {
deltaValue = (row.ack_time - row.start_time);
caseValue = 'C.0';
};
var ack = new ackModel({
hostgroup : row.hostgroup,
host : row.hostname,
service : row.servicename,
timePeriod : row.timeperiod,
startTime : row.start_time,
ackTime : row.ack_time,
state : row.state,
deltaTime : deltaValue,
caseNumb : caseValue,
author : row.author,
ackId : row.ack_id
});
console.log(ack);
ack.save(function (err, ack) {
if (err) {
console.log(getTimeStamp() + 'Mongoose .save error : ' + err);
}
else {
console.log(getTimeStamp() + 'SAVE Mongoose : ' + ack.author + ' ' + ack.ackId);
}
});
});
callback(docs);
});
};
As you can see i'm fetching some raws from a MySQL databse to put them into a mongo database. The problem is that ack.save() doesn't save anything when the ack var is perfectly ready to be saved.
This is how ack is filled (from console.log(ack) ) :
{ _id: 568d360867e31d11001206f7,
ackId: 1087,
author: 'pilote1',
caseNumb: 'C.10',
deltaTime: -3481,
state: 2,
ackTime: 1452091450,
startTime: 1452094931,
timePeriod: 'RESSOURCES-GPE-N1-8/20',
service: 'Service-Random-1M',
host: 'PRO_HOST3',
hostgroup: 'PROSERVIA' }