I have a custom model and I want to add a validation in the _beforeSave() method so that if it's a new object, and no customer_id has been set, it shouldn't save the record at all. I did the validations on my pages but that doesn't keep other developers from doing something like:

$myModel = Mage::getModel("myModule/myModel");
$myModel->save();

This shouldn't happen because some values must be set before saving. I want something like:

public function _beforeSave()
{
    parent::_beforeSave();
    if($this->getCustomerId() <= 0)
    {
         #cancel save
    }

    return $this;
}

Can I cancel the save() method?