Check if product exists before saving

Try this code to detect is product exist or not:

$productId = $this->getRequest()->getParam('product_id'); // change to your product id real param name $productExists = true; try { $product = $this->productRepository->getById($productId); } catch (\Magento\Framework\Exception\NoSuchEntityException $e) { $productExists = false; } 

PS: it requires the product id (from the request). Do not forget to replace the 'product_id parameter name to the real one you are using in the form.

Here is a full code with a modification:

<?php /** * Created by PhpStorm. * User: magebit * Date: 18.4.1 * Time: 16:05 */ namespace Magebit\ProductComments\Controller\Adminhtml\Comments; use Magento\Backend\App\Action; use Magebit\ProductComments\Model\Comments; use Magento\Catalog\Api\ProductRepositoryInterface; class Save extends Action { /** * @var \Magento\Catalog\Api\ProductRepositoryInterface */ private $productRepository; protected $_model; /** * Save constructor. * * @param Action\Context $context * @param Comments $model * @param ProductRepositoryInterface $productRepository */ public function __construct( Action\Context $context, Comments $model, ProductRepositoryInterface $productRepository ) { parent::__construct($context); $this->_model = $model; $this->productRepository = $productRepository; } /** * Save action * * @return \Magento\Framework\Controller\ResultInterface * @throws \Magento\Framework\Exception\NoSuchEntityException */ public function execute() { $data = $this->getRequest()->getPostValue(); /** @var \Magento\Backend\Model\View\Result\Redirect $resultRedirect */ $resultRedirect = $this->resultRedirectFactory->create(); if ($data) { $productId = $this->getRequest()->getParam('product_id'); // change to your product id real param name try { $this->productRepository->getById($productId); } catch (\Magento\Framework\Exception\NoSuchEntityException $e) { // In case there is no product: display error message and redirect back $this->messageManager->addError($e->getMessage()); $this->_getSession()->setFormData($data); return $resultRedirect->setPath('*/*/edit', ['comment_id' => $this->getRequest()->getParam('id')]); } /** @var \Magebit\ProductComments\Model\Comments $model */ $model = $this->_model; $id = $this->getRequest()->getParam('id'); if ($id) { $model->load($id); } $model->setData($data); $this->_eventManager->dispatch( 'productcomments_comments_prepare_save', ['comments' => $model, 'request' => $this->getRequest()] ); var_dump($productId); try { $model->save(); $this->messageManager->addSuccess(__('Comment successfully saved')); $this->_getSession()->setFormData(false); if ($this->getRequest()->getParam('back')) { return $resultRedirect->setPath('*/*/edit', ['id' => $model->getId(), '_current' => true]); } return $resultRedirect->setPath('*/*/'); } catch (\Magento\Framework\Exception\LocalizedException $e) { $this->messageManager->addError($e->getMessage()); } catch (\RuntimeException $e) { $this->messageManager->addError($e->getMessage()); } catch (\Exception $e) { $this->messageManager->addException($e, __('Something went wrong while saving the comment')); } $this->_getSession()->setFormData($data); return $resultRedirect->setPath('*/*/edit', ['comment_id' => $this->getRequest()->getParam('id')]); } return $resultRedirect->setPath('*/*/'); } } 

Before we doing something with a model we try to load corresponding product from the repository. In case there was no product, the NoSuchEntityException exception throws and we redirecting the customer to the previous page and displaying the error message, like "There was no product with id ...".