Error message not display

[diego]

Hi everyone, I'm modifying the controller AdminProductController.php to do some controls on the BO side on SKU. However, I have the problem of showing an error message to the user when a condition occurs on the update of the product, but this is not displayed.

What I do now is this:

I modified the file controller-> admin-> AdminProductController.php adding this function

public function checkUniqueRef()
	{
		$reference = Tools::getValue('reference');
		$idproduct = Tools::getValue('id_product');
		if ($reference!=""){
			$sql = 'SELECT id_product FROM `'._DB_PREFIX_.'product` WHERE reference="'.$reference.'" AND id_product<>'.$idproduct;
			$res = Db::getInstance()->getValue($sql);
			if($res)
			{
			    $this->errors[] = $this->trans('Product with this reference is already exists.', array(), 'Admin.Notifications.Error');
			    //alternative
				//$this->errors[] = sprintf(Tools::displayError('Product with reference %s is already exists.'), $reference);
			}
		}
	}

and i call here:

public function checkProduct()
    {
     
		$this->checkUniqueRef();
		if (!empty($this->errors)) {
            $this->display = 'update';
            return false;
        }

however, if the error is found, the error message is not displayed, but the success message for the update is displayed. If I insert an echo ("hello") statement inside the condition

if ($ res) {....}

a generic error is displayed that is not for me.

Do you have any suggestions? thanks in advance to those who want to help me!