Ttdfjt

when I have the category in product assign and saving category below error showing

The value specified in the URL Key field would generate a URL that
already exists.

To resolve this conflict, you can either change the
value of the URL Key field (located in the Search Engine Optimization
section) to a unique value or change the Request Path fields in all
locations listed below:

and my exception.log error log is

Please override with below two files :
module-catalog-url-rewrite/Model/Product/AnchorUrlRewriteGenerator.php (Line 58)

/**
 * Generate list based on categories
 *
 * @param int $storeId
 * @param Product $product
 * @param ObjectRegistry $productCategories
 * @return UrlRewrite[]
 */
 public function generate($storeId, Product $product, ObjectRegistry $productCategories)
 
 $urls = [];
 foreach ($productCategories->getList() as $category) 
 $anchorCategoryIds = $category->getAnchorsAbove();
 if ($anchorCategoryIds) 
 foreach ($anchorCategoryIds as $anchorCategoryId) 
 //Default: $anchorCategory = $this->categoryRepository->get($anchorCategoryId);
 $anchorCategory = $this->categoryRepository->get($anchorCategoryId, $storeId);
 $urls[] = $this->urlRewriteFactory->create()
 ->setEntityType(ProductUrlRewriteGenerator::ENTITY_TYPE)
 ->setEntityId($product->getId())
 ->setRequestPath(
 $this->urlPathGenerator->getUrlPathWithSuffix(
 $product,
 $storeId,
 $anchorCategory
 )
 )
 ->setTargetPath(
 $this->urlPathGenerator->getCanonicalUrlPath(
 $product,
 $anchorCategory
 )
 )
 ->setStoreId($storeId)
 ->setMetadata(['category_id' => $anchorCategory->getId()]);
 
 
 
return $urls;
 

step2 : module-catalog-url-rewrite/Model/ProductUrlRewriteGenerator.php (Line 146)

/**
 * Generate list of urls for global scope
 *
 * @param MagentoFrameworkDataCollection $productCategories
 *
 * @return MagentoUrlRewriteServiceV1DataUrlRewrite[]
 */
 protected function generateForGlobalScope($productCategories)
 
 $urls = [];
 $productId = $this->product->getEntityId();
 foreach ($this->product->getStoreIds() as $id) 
 if (!$this->isGlobalScope($id)
 && !$this->storeViewService->doesEntityHaveOverriddenUrlKeyForStore($id, $productId, Product::ENTITY)
 ) 
 // Default: $urls = array_merge($urls, $this->generateForSpecificStoreView($id, $productCategories));
 // before loading the category collection by looping it, clone it and set the correct store id,
 // so we get the correct url_path & url_key for that specific store id
 $storeSpecificProductCategories = clone $productCategories;
 $storeSpecificProductCategories->setStoreId($id);
 $urls = array_merge($urls, $this->generateForSpecificStoreView($id, $storeSpecificProductCategories));
 
 
 return $urls;
 

1 Run the following SQL queries from the command line or phpMyAdmin,

SET FOREIGN_KEY_CHECKS = 0; 
TRUNCATE TABLE url_rewrite; 
SET FOREIGN_KEY_CHECKS = 1;

2 Within your backend, navigate to Products > Catalog.

3.Clear any and all filters, select all products (drop down menu option Select All).

4 Select the Update Attributes action from the Actions dropdown menu.

5 Under Products Information, click the Websites tab.

6 Under the Add Product to Websites section, check the box for Main Website (and
any other sites you may have)

7 Click Save.

8 Navigate to Products > Categores.

9 For each category you want to have a new URL key written, select it, update the URL key, ensure that the Create Permanent Redirect for Old URL checkbox is checked.

10 Click Save.

There are so may issue is already reported on stack & GitHub and other community. and there are so many solutions for that and which one is correct it is to difficult choosing the right one. but I see one issue is reported on GitHub which one help to you I think. https://github.com/magento/magento2/issues/7298

This issue occurring due to duplicate entry on the database table url_rewrite, so there is only one way to resolve this issue you need to empty the table and regenerate the URL. so I have checked and found one answer which one usefull to me which I shared below.

Note: Take database backup before doing below opration.

Remove the duplication data when saving category. This data is throw in method doReplace($urls) in vendormagentomodule-url-rewriteModelStorageDbStorage.php file.

protected function doReplace($urls)

 foreach ($this->createFilterDataBasedOnUrls($urls) as $type => $urlData) 
 $urlData[UrlRewrite::ENTITY_TYPE] = $type;
 $this->deleteByData($urlData);
 
 $data = [];
 foreach ($urls as $url) 
 $data[] = $url->toArray();
 
 $this->insertMultiple($data);

I found out $data variable has a duplicate record. If you want this method to work without any errors. Rewrite this method above to below one.

protected function doReplace($urls) 
 foreach ($this->createFilterDataBasedOnUrls($urls) as $type => $urlData) 
 $urlData[UrlRewrite::ENTITY_TYPE] = $type;
 $this->deleteByData($urlData);
 
 $data = [];
 $storeId_requestPaths = [];
 foreach ($urls as $url) 
 $storeId = $url->getStoreId();
 $requestPath = $url->getRequestPath();
 // Skip if is exist in the database
 $sql = "SELECT * FROM url_rewrite where store_id = $storeId and request_path = '$requestPath'";
 $exists = $this->connection->fetchOne($sql);

 if ($exists) continue;

 $storeId_requestPaths[] = $storeId . '-' . $requestPath;
 $data[] = $url->toArray();
 

 // Remove duplication data;
 $n = count($storeId_requestPaths);
 for ($i = 0; $i < $n - 1; $i++) 
 for ($j = $i + 1; $j < $n; $j++) 
 if ($storeId_requestPaths[$i] == $storeId_requestPaths[$j]) 
 unset($data[$j]);
 
 
 
 $this->insertMultiple($data); 

Taje refrance from Magento 2 Duplicate Product URLs Problem And "URL key for specified store already exists." cannot save category #7298
I hope it helps!