HI, i'm looking for a way to extend POS using model.js

I have wroted this function inside Order.extend

get_tiquete_hacienda: function (){
 var rpc2 = require('web.rpc');
 rpc2.query({
 model: 'pos.order',
 method: 'compute_sales_bsi'
 }).then(function(res) {
 this.consecutivo = res;
 console.log('soy el otro: ' + res);
 });

 return this.consecutivo;
}

When creating a new order, if a look at the console the value "soy el otro" shows the data but the variable "consecutivo" inside order data shows "undefined"

What i'm doing wrong?