MAGETWO-59315: Non consistent save Product Stock Item via Web API and repository directly

Author: Yaroslav Onischenko

app/code/Magento/Catalog/Model/Product/Attribute/Backend/Stock.php

@@ -59,7 +59,7 @@ public function beforeSave($object)
         if (isset($stockData['qty']) && $stockData['qty'] === '') {
             $stockData['qty'] = null;
         }
-        if ($object->getStockData() !== null || $stockData !== null) {
+        if ($object->getStockData() !== null && $stockData !== null) {
             $object->setStockData(array_replace((array)$object->getStockData(), (array)$stockData));
         }
         $object->unsetData($this->getAttribute()->getAttributeCode());

app/code/Magento/Catalog/Test/Unit/Model/Product/Attribute/Backend/StockTest.php

@@ -125,4 +125,17 @@ public function testBeforeSaveQtyIsZero()
         $stockData = $object->getStockData();
         $this->assertEquals(0, $stockData['qty']);
     }
+
+    public function testBeforeSaveNoStockData()
+    {
+        $object = new \Magento\Framework\DataObject(
+            [
+                self::ATTRIBUTE_NAME => ['is_in_stock' => 1, 'qty' => 0]
+            ]
+        );
+
+        $this->model->beforeSave($object);
+        $this->assertNull($object->getStockData());
+        $this->assertNull($object->getData(self::ATTRIBUTE_NAME));
+    }
 }

dev/tests/integration/testsuite/Magento/CatalogInventory/Api/StockItemSaveTest.php

@@ -0,0 +1,43 @@
+<?php
+/**
+ * Copyright © 2016 Magento. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+namespace Magento\CatalogInventory\Api;
+
+use Magento\Catalog\Api\Data\ProductExtensionInterface;
+use Magento\Catalog\Api\Data\ProductInterface;
+use Magento\Catalog\Api\ProductRepositoryInterface;
+
+class StockItemSaveTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @magentoDataFixture Magento/Catalog/_files/product_simple.php
+     */
+    public function testSave()
+    {
+        $objectManager = \Magento\TestFramework\Helper\Bootstrap::getObjectManager();
+        /** @var ProductRepositoryInterface $productRepository */
+        $productRepository = $objectManager->get(ProductRepositoryInterface::class);
+        /** @var ProductInterface $product */
+        $product = $productRepository->get('simple');
+
+        /** @var ProductExtensionInterface $ea */
+        $ea = $product->getExtensionAttributes();
+        $ea->getStockItem()->setQty(555);
+        $productRepository->save($product);
+
+        $product = $productRepository->get('simple');
+        $this->assertEquals(555, $product->getExtensionAttributes()->getStockItem()->getQty());
+
+        $stockItem = $product->getExtensionAttributes()->getStockItem();
+        $stockItem->setQty(200);
+        /** @var StockItemRepositoryInterface $stockItemRepository */
+        $stockItemRepository = $objectManager->get(StockItemRepositoryInterface::class);
+        $stockItemRepository->save($stockItem);
+        $this->assertEquals(200, $product->getExtensionAttributes()->getStockItem()->getQty());
+
+        $product = $productRepository->get('simple');
+        $this->assertEquals(200, $product->getExtensionAttributes()->getStockItem()->getQty());
+    }
+}