MAGETWO-50123: Unable to assign blank value to attribute #3545 #4910 #5485

Author: Mykola Palamar

app/code/Magento/Catalog/Ui/DataProvider/Product/Form/Modifier/Eav.php

@@ -522,6 +522,45 @@ private function getPreviousSetAttributes()
         return $this->prevSetAttributes;
     }
 
+    /**
+     * Check is product already exists or we trying to create one
+     *
+     * @return bool
+     */
+    private function isProductExists()
+    {
+        return (bool) $this->locator->getProduct()->getId();
+    }
+
+    /**
+     * Check is product has some value for attribute
+     *
+     * @param ProductAttributeInterface $attribute
+     * @return bool
+     */
+    private function isProductHasValueForAttribute(ProductAttributeInterface $attribute)
+    {
+        return (bool)($this->locator->getProduct()->getCustomAttribute($attribute->getAttributeCode()) !== null)
+            && $this->locator->getProduct()->getCustomAttribute($attribute->getAttributeCode())->getValue();
+    }
+
+    /**
+     * Check should we display default values for attribute or not
+     *
+     * @param ProductAttributeInterface $attribute
+     * @return bool
+     */
+    private function isShowDefaultValue(ProductAttributeInterface $attribute)
+    {
+        if (!$this->isProductExists()) {
+            return true;
+        } elseif ($attribute->getIsRequired() && !$this->isProductHasValueForAttribute($attribute)) {
+            return true;
+        }
+
+        return false;
+    }
+
     /**
      * Initial meta setup
      *
@@ -543,7 +582,7 @@ public function setupAttributeMeta(ProductAttributeInterface $attribute, $groupC
             'visible' => $attribute->getIsVisible(),
             'required' => $attribute->getIsRequired(),
             'notice' => $attribute->getNote(),
-            'default' => $attribute->getDefaultValue(),
+            'default' => $this->isShowDefaultValue($attribute) ? $attribute->getDefaultValue() : null,
             'label' => $attribute->getDefaultFrontendLabel(),
             'code' => $attribute->getAttributeCode(),
             'source' => $groupCode,

app/code/Magento/Eav/Model/Entity/Attribute.php

@@ -167,6 +167,15 @@ protected function _getDefaultBackendModel()
                 break;
         }
 
+        // we should override default behaviour of Magento\Framework\Exception\LocalizedException\AbstractBackend
+        // but can't do this in abstract model and can't update DB records because of backward compatibility
+        if ($this->getFrontendInput() == 'select'
+            && !$this->getIsRequired()
+            && !$this->getBackendModel()
+        ) {
+            return \Magento\Eav\Model\Entity\Attribute\Backend\SelectBackend::class;
+        }
+
         return parent::_getDefaultBackendModel();
     }
 

app/code/Magento/Eav/Model/Entity/Attribute/Backend/SelectBackend.php

@@ -0,0 +1,22 @@
+<?php
+/**
+ * Copyright © 2016 Magento. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+namespace Magento\Eav\Model\Entity\Attribute\Backend;
+
+/**
+ * Entity/Attribute/Model - attribute backend default
+ *
+ * @author      Magento Core Team <core@magentocommerce.com>
+ */
+class SelectBackend extends \Magento\Eav\Model\Entity\Attribute\Backend\AbstractBackend
+{
+
+    public function beforeSave($object)
+    {
+        return $this;
+
+    }
+}
+