MAGETWO-87588: Fix json encoded attribute backend type to not encode attribute value multiple times magento#13551

 - Merge Pull Request magento#13551 from tkotosz/magento2:patch-5
 - Merged commits:
   1. 85f36cd
   2. 3d10764

Author: Oleksii Korshenko

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

@@ -41,7 +41,7 @@ public function beforeSave($object)
     {
         // parent::beforeSave() is not called intentionally
         $attrCode = $this->getAttribute()->getAttributeCode();
-        if ($object->hasData($attrCode)) {
+        if ($object->hasData($attrCode) && !is_string($object->getData($attrCode))) {
             $object->setData($attrCode, $this->jsonSerializer->serialize($object->getData($attrCode)));
         }
         return $this;

app/code/Magento/Eav/Test/Unit/Model/Entity/Attribute/Backend/JsonEncodedTest.php

@@ -82,6 +82,25 @@ public function testBeforeSave()
         $this->assertEquals(json_encode([1, 2, 3]), $product->getData('json_encoded'));
     }
 
+    /**
+     * Test before save handler with already encoded attribute value
+     */
+    public function testBeforeSaveWithAlreadyEncodedValue()
+    {
+        $product = new \Magento\Framework\DataObject(
+            [
+                'json_encoded' => [1, 2, 3]
+            ]
+        );
+
+        // save twice
+        $this->model->beforeSave($product);
+        $this->model->beforeSave($product);
+        
+        // check it is encoded only once
+        $this->assertEquals(json_encode([1, 2, 3]), $product->getData('json_encoded'));
+    }
+
     /**
      * Test after load handler
      */