ENGCOM-2319: #96 Make category query compatible with staging #99

 - Merge Pull Request magento/graphql-ce#99 from magento/graphql-ce:96-compatibility-with-content-staging
 - Merged commits:
   1. e79f381

Author: magento-engcom-team

app/code/Magento/CatalogGraphQl/Model/Resolver/Products/DataProvider/CategoryTree.php

@@ -100,7 +100,7 @@ public function getTree(ResolveInfo $resolveInfo, int $rootCategoryId) : array
         $collection->addFieldToFilter('level', ['lteq' => $level + $depth - self::DEPTH_OFFSET]);
         $collection->setOrder('level');
         $collection->getSelect()->orWhere(
-            $this->metadata->getMetadata(CategoryInterface::class)->getLinkField() . ' = ?',
+            $this->metadata->getMetadata(CategoryInterface::class)->getIdentifierField() . ' = ?',
             $rootCategoryId
         );
         return $this->processTree($collection->getIterator());

dev/tests/api-functional/testsuite/Magento/GraphQl/Catalog/CategoryTest.php

@@ -8,6 +8,7 @@
 namespace Magento\GraphQl\Catalog;
 
 use Magento\Catalog\Api\Data\CategoryInterface;
+use Magento\Catalog\Model\ResourceModel\Category\Collection as CategoryCollection;
 use Magento\Framework\DataObject;
 use Magento\TestFramework\TestCase\GraphQlAbstract;
 use Magento\Catalog\Api\Data\ProductInterface;
@@ -286,16 +287,13 @@ public function testCategoryProducts()
      */
     public function testAnchorCategory()
     {
-        /** @var \Magento\Catalog\Model\ResourceModel\Category\Collection $categoryCollection */
-        $categoryCollection = $this->objectManager->create(
-            \Magento\Catalog\Model\ResourceModel\Category\Collection::class
-        );
+        /** @var CategoryCollection $categoryCollection */
+        $categoryCollection = $this->objectManager->create(CategoryCollection::class);
         $categoryCollection->addFieldToFilter('name', 'Category 1');
+        /** @var CategoryInterface $category */
         $category = $categoryCollection->getFirstItem();
-        /** @var \Magento\Framework\EntityManager\MetadataPool $entityManagerMetadataPool */
-        $entityManagerMetadataPool = $this->objectManager->create(\Magento\Framework\EntityManager\MetadataPool::class);
-        $categoryLinkField = $entityManagerMetadataPool->getMetadata(CategoryInterface::class)->getLinkField();
-        $categoryId = $category->getData($categoryLinkField);
+        $categoryId = $category->getId();
+
         $this->assertNotEmpty($categoryId, "Preconditions failed: category is not available.");
 
         $query = <<<QUERY