/**
* Delete all invoice data from database and the file.
*/
public function delete()
{
// remove all invoice data from db
delete_post_meta($this->order->id, '_bewpi_invoice_number');
delete_post_meta($this->order->id, '_bewpi_formatted_invoice_number');
delete_post_meta($this->order->id, '_bewpi_invoice_date');
delete_post_meta($this->order->id, '_bewpi_invoice_year');
// delete file
if ($this->exists()) {
parent::delete();
}
}