Yii on update, detect if a specific AR property has been changed on beforeSave()

Question

I am raising a Yii event on beforeSave of the model, which should only be fired if a specific property of the model is changed.

The only way I can think of how to do this at the moment is by creating a new AR object and querying the DB for the old model using the current PK, but this is not very well optimized.

Here's what I have right now (note that my table doesn't have a PK, that's why I query by all attributes, besides the one I am comparing against - hence the unset function):

public function beforeSave()
{
    if(!$this->isNewRecord){ // only when a record is modified
        $newAttributes = $this->attributes;
        unset($newAttributes['level']);
        $oldModel = self::model()->findByAttributes($newAttributes);

        if($oldModel->level != $this->level)
            // Raising event here
    }
    return parent::beforeSave();
}

Is there a better approach? Maybe storing the old properties in a new local property in afterFind()?

Answer 1

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();
}