You need to store the old attributes in a local property in the AR class so that you can compare the current attributes to those old ones at any time.
Step 1. Add a new property to the AR class:
// Stores old attributes on afterFind() so we can compare
// against them before/after save
protected $oldAttributes;
Step 2. Override Yii's afterFind()
and store the original attributes immediately after they are retrieved.
public function afterFind(){
$this->oldAttributes = $this->attributes;
return parent::afterFind();
}
Step 3. Compare the old and new attributes in beforeSave/afterSave
or anywhere else you like inside the AR class. In the example below we are checking if the property called 'level' is changed.
public function beforeSave()
{
if(isset($this->oldAttributes['level']) && $this->level != $this->oldAttributes['level']){
// The attribute is changed. Do something here...
}
return parent::beforeSave();
}