Adapting Yii 1.x models to allow change validation

SomeModel.php

<?php

class SomeModel extends GxActiveRecord
{
    /**
     * @var $oldAttributes Holds the state of the object afterFind() until afterSave()
     */
    protected $oldAttributes;
    
    /**
     * Yii hook after filling the model
     */
    public function afterFind()
    {
        $this->oldAttributes = $this->attributes;
        return parent::afterFind();
    }
    
    /**
     * Yii hook after saving (create or update) the model
     */
    public function afterSave()
    {
        $this->oldAttributes = $this->attributes;
        return parent::afterSave();
    }
    
    /**
     * Example on how to use the $oldAttributes to check for 
     * changes in the model beforeSave().
     * You should do this on Yii using rules() and creating a validation 
     * method, but to keep things short and easily to understand...
     *
     * @return boolean 
     */
    public function beforeSave()
    {
        // first check if it is not a new record
        if (!$this->isNewRecord) {
            // check if 'created_date' attribute has changed
            if ($this->oldAttributes['created_date'] != $this->created_date) {
                $this->addError('created_date', "You can't change the created date!");
            }
        }
        
        return $this->hasErrors();
    }
}