I am creating a frontend from for Sellers to add/edit their product on website, product adding/editing is working perfect. Now I have to assign that product to a category

Almost on every article and blog there is one proper solution to assign product to a category:

//Removing previous categories
$previousCategoryIds = $product->getCategoryIds();
foreach($previousCategoryIds as $k=>$previousCategoryId){

//Assigning new categories

The code is fine, but I am getting this error:

Fatal error: Uncaught Error: Call to undefined method Magento\Catalog\Model\ResourceModel\Category\Flat::saveAttribute() in ...vendor/magento/module-catalog-url-rewrite/Observer/CategoryUrlPathAutogeneratorObserver.php:96

I have searched this error and found the cause of this error:

The problem is, category link repository and link management is only for backend, and I am trying to use it on frontend scope that's why it is causing this error.

I have also tried this:


But above code appending categories, not replacing previous categories.

Can you help me resolve this issue? I have tried everything I have found.


The problem is with flat category, if I enable flat category then error occurs, and if I disable flat category it is working fine.

  • which magento version you used? any other category related extension are there? Oct 16, 2019 at 6:00
  • no other category extension. And I am using magento 2.2.8. Please see tags that I have attached Oct 16, 2019 at 6:07

1 Answer 1


can you try this code it's works for me

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();

$CategoryLinkRepository = $objectManager->get('\Magento\Catalog\Model\CategoryLinkRepository');

$categoryId = 4;
$sku = 'Jacket';


$categoryIds = [3]; // your category ids Array like [2,3,5]
$product = $objectManager->get('Magento\Catalog\Model\Product')->loadByAttribute('sku', $sku);
  • I have tried same thing, but getting error on this: $CategoryLinkRepository->deleteByIds($categoryId,$sku); please check question Oct 16, 2019 at 5:53
  • i have tested code in magento 2.2.8 but i'm not getting any errors. Oct 16, 2019 at 6:35
  • Have you tried this on frontend or backend? is that you custom script or you are doing it in controller? Oct 16, 2019 at 6:36
  • on frontend using custom root script for testing Oct 16, 2019 at 6:41
  • that's it mate :). In custom script you can define scope of file like adminhtml or cronjob etc. But in frontend controller it would cause issue, this is what I am facing :( Oct 16, 2019 at 6:52

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