Mongoose : update a document in a pre save hook - node.js

Question

i'm quite new to nodeJS and have some problem i cannot solve...
i would like to update a related document in a pre save hook in mongoose :
No errors, but as a result i always get:
updated:{"n":1,"nModified":0,"ok":1}
so document is never updated.... how can i solve this ? i know i can make all controls before, but pre-hook seems the good place for that.
thanks for your help...
var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var suivilotSchema = new Schema({
code_lot: { type: String,Required: 'Code Lot cannot be left blank.' },
site_IMS: { type: String,Required: 'Site IMS cannot be left blank'},
date_plantws: { type: String,Required: 'tws plan prod cannot be left blank'},
nb_server: { type: Number,Required: 'nb Server cannot be left blank.',default: 1},
nb_server_done: { type: Number,Required: 'nb Server done cannot be left blank.',default: 0},
date_created: { type: Date,default: Date.now },
date_updated: { type: Date },
retry: { type: Number },
status: { type: Number}
});
suivilotSchema.pre('save', function (next) {
console.log('***** PRE HOOK suivilot *******');
var self = this;
this.constructor.findOne({'code_lot' : self.code_lot,'date_plantws' : self.date_plantws, 'retry' :
self.retry },function (err,existinglot) {
if (!existinglot){
console.log('SUIVILOTS : pas de resultat');
next();
}
else{
console.log('SUIVILOTS : lot exists: ',existinglot._id);
existinglot.updateOne({ '_id' : existinglot._id }, { $inc:{'nb_server' : 1}
},function(err,updated){
if(err)
console.log("Error during increment server :"+err);
console.log('updated:'+JSON.stringify(updated));
console.log('updated:'+JSON.stringify(existinglot));
});
}
});
});