MC-21727: It is impossible to remove Related, Up-Sells and Cross-Sells products via the import procedure

Author: Oleksandr Iegorov

app/code/Magento/CatalogImportExport/Model/Import/Product.php

@@ -1198,7 +1198,7 @@ protected function _initTypeModels()
             // phpcs:disable Magento2.Performance.ForeachArrayMerge.ForeachArrayMerge
             $this->_fieldsMap = array_merge($this->_fieldsMap, $model->getCustomFieldsMapping());
             $this->_specialAttributes = array_merge($this->_specialAttributes, $model->getParticularAttributes());
-            // phpcs:enable 
+            // phpcs:enable
         }
         $this->_initErrorTemplates();
         // remove doubles
@@ -3060,6 +3060,7 @@ private function getValidationErrorLevel($sku): string
      * @param int $nextLinkId
      * @param array $positionAttrId
      * @return void
+     * @throws LocalizedException
      */
     private function processLinkBunches(
         array $bunch,
@@ -3070,6 +3071,7 @@ private function processLinkBunches(
         $productIds = [];
         $linkRows = [];
         $positionRows = [];
+        $linksToDelete = [];
 
         $bunch = array_filter($bunch, [$this, 'isRowAllowedToImport'], ARRAY_FILTER_USE_BOTH);
         foreach ($bunch as $rowData) {
@@ -3086,10 +3088,15 @@ function ($linkName) use ($rowData) {
             );
             foreach ($linkNameToId as $linkName => $linkId) {
                 $linkSkus = explode($this->getMultipleValueSeparator(), $rowData[$linkName . 'sku']);
+                //process empty value
+                if (!empty($linkSkus[0]) && $linkSkus[0] === Import::DEFAULT_EMPTY_ATTRIBUTE_VALUE_CONSTANT) {
+                    $linksToDelete[$linkId][] = $productId;
+                    continue;
+                }
+
                 $linkPositions = !empty($rowData[$linkName . 'position'])
                     ? explode($this->getMultipleValueSeparator(), $rowData[$linkName . 'position'])
                     : [];
-
                 $linkSkus = array_filter(
                     $linkSkus,
                     function ($linkedSku) use ($sku) {
@@ -3098,6 +3105,7 @@ function ($linkedSku) use ($sku) {
                             && strcasecmp($linkedSku, $sku) !== 0;
                     }
                 );
+
                 foreach ($linkSkus as $linkedKey => $linkedSku) {
                     $linkedId = $this->getProductLinkedId($linkedSku);
                     if ($linkedId == null) {
@@ -3129,9 +3137,33 @@ function ($linkedSku) use ($sku) {
                 }
             }
         }
+        $this->deleteProductsLinks($resource, $linksToDelete);
         $this->saveLinksData($resource, $productIds, $linkRows, $positionRows);
     }
 
+    /**
+     * Delete links
+     *
+     * @param Link $resource
+     * @param array $linksToDelete
+     * @return void
+     * @throws LocalizedException
+     */
+    private function deleteProductsLinks(Link $resource, array $linksToDelete) {
+        if (!empty($linksToDelete) && Import::BEHAVIOR_APPEND === $this->getBehavior()) {
+            foreach ($linksToDelete as $linkTypeId => $productIds) {
+                if (!empty($productIds)) {
+                    $whereLinkId = $this->_connection->quoteInto('link_type_id', $linkTypeId);
+                    $whereProductId =  $this->_connection->quoteInto('product_id IN (?)', array_unique($productIds));
+                    $this->_connection->delete(
+                        $resource->getMainTable(),
+                        $whereLinkId . ' AND ' . $whereProductId
+                    );
+                }
+            }
+        }
+    }
+
     /**
      * Fetches Product Links
      *