How in Yii2 in the model to determine whether the values ​​have changed?

Question

Yii

If the values ​​have changed, then you need to perform certain actions in afterSave().
Is it possible?
update:
Model - ActiveRecord.

Answer 1

Maxim Fedorov gave a good option, I'll add a less correct one, but it will work in yii\base\Model
Add the public $old_value variable to the model, assign a value in afterFind, then check aftersave