_data = array( 'name' => null, 'price' => null, 'quantity' => 1, 'sku' => null ); } private function _check_required_fields() { if(empty($this->_data['name'])) { $this->add_error('item name is required.'); } if(!is_numeric($this->_data['price'])) { $this->add_error('price must be a number.'); } } private function _check_quantity() { if($this->_data['quantity'] < 1) { $this->add_error('quantity must be greater than or equal to 1'); } } public function __construct() { $this->_init(); } public function __get($key) { $value = false; if($key == 'total') { $value = $this->_data['price'] * $this->_data['quantity']; $value = number_format($value, 2, '.', ''); } else { $value = parent::__get($key); } return $value; } public function get_data() { $data = parent::get_data(); $data['total'] = $this->total; return $data; } public function validate() { $this->_check_required_fields(); $this->_check_quantity(); return count($this->_errors) == 0; } }