Bringing computable model fields to ExtJS

computed-model-field.extjs.js

// All creadits gouse to 
// http://flexblog.faratasystems.com/2012/02/07/computed-fields-in-extjs-models-via-convert-functions
Ext.define('Sample.model.User', {
    extend: 'Ext.data.Model',
    fields: [
       { name:'id', type:'string' },
       { name:'firstName', type:'string' },
       { name:'lastName', type:'string' },
       { 
            name:'fullName', 
            type:'string',
            convert: function (newValue, model) {
               return model.get('lastName') + ',  ' + model.get('firstName');
            }
       }
    ],
    set: function(fieldName, value) {
      this.callParent(arguments);
      if (fieldName === 'firstName' || fieldName === 'lastName') {
        this.set('fullName');
      }
    }
});