Fat Free Framework: Can I setup a model to compute a field value before save?

Is there a way for the model to compute a field before save?

I have a schema something like this:

item_id
item_qty
item_price
linetotal

I'm trying to avoid this kind of code in my controller:

$model->linetotal = $f3->get('POST.item_qty') * $f3->get('POST.item_price');
$model->save();

Instead, I want to setup my model to compute the linetotal before save.

Perhaps something like the beforeSave callback in cakephp, or even better maybe I missed that I can set it up just like a Mapper virtual field on f3, except its a real field...

What you're asking for has just been released in 3.2.2. DB mappers now come with the following hooks: beforeinsert, afterinsert, beforeupdate, afterupdate, beforeerase, aftererase and onload.

So you could implement the linetotal calculation like this:

class myModel extends \DB\SQL\Mapper {

  static function _beforeupdate($self,$pkeys) {
    $self->linetotal = $self->item_qty * $self->item_price;
  }

  function __construct() {
    $f3=\Base::instance();
    parent::construct($f3->get('DB'),'mytable');
    $this->beforeupdate(array(__CLASS__,'_beforeupdate'));
  }

}

But since the calculation is also relevant for INSERT statements, you'll also need to hook the beforeinsert event. You could use the same function to hook both events :

class myModel extends \DB\SQL\Mapper {

  static function _linetotal($self,$pkeys) {
    $self->linetotal = $self->item_qty * $self->item_price;
  }

  function __construct() {
    $f3=\Base::instance();
    parent::construct($f3->get('DB'),'mytable');
    $this->beforeinsert(array(__CLASS__,'_linetotal'));
    $this->beforeupdate(array(__CLASS__,'_linetotal'));
  }

}

NB: an alternative way to implement the linetotal calculation would be to simply override the mapper set() method:

class myModel extends \DB\SQL\Mapper {

  function set($key,$val) {
    parent::set($key,$val);
    if ($key=='item_qty' || $key=='item_price')
      $this->linetotal = $this->item_qty * $this->item_price;
  }

}

EDIT:

I forgot a third alternative, which actually looks more appropriate in your case: virtual fields. In this case, the calculation is left to the DB engine. E.g:

class myModel extends \DB\SQL\Mapper {

  function __construct(){
    $f3=\Base::instance();
    parent::construct($f3->get('DB'),'mytable');
    $this->linetotal = 'item_qty * item_price';
  }

}

PS: don't forget to remove the linetotal field from your database.