AC-10042::/V1/transactions REST API returns error when parent_txn_id = txn_id

Author: AshishKumarPundeer

app/code/Magento/Sales/Model/ResourceModel/Order/Payment/Transaction.php

@@ -146,6 +146,15 @@ protected function _beforeSave(\Magento\Framework\Model\AbstractModel $transacti
                     __('We don\'t have enough information to save the parent transaction ID.')
                 );
             }
+            /*$parentId = (int)$this->_lookupByTxnId($orderId, $paymentId, $parentTxnId, $idFieldName);
+            if ($parentId) {
+                $transaction->setData('parent_id', $parentId);
+            }*/
+        } else {
+            $oldParentTxnId = $this->getParentTxnId($orderId);
+            if($oldParentTxnId) {
+                $transaction->setData('parent_txn_id', $oldParentTxnId);
+            }
         }
 
         // make sure unique key won't cause trouble
@@ -207,4 +216,19 @@ private function _getLoadByUniqueKeySelect($orderId, $paymentId, $txnId, $column
             $txnId
         );
     }
+    /**
+     * Retrieve transaction by the unique key of order_id
+     * @param int $orderId
+     */
+    protected function getParentTxnId($orderId) {
+        $connection = $this->getConnection();
+        $select = $connection->select()->from(
+            $this->getMainTable(),
+            ['parent_txn_id']
+        )->where(
+            'order_id = ?',
+            $orderId
+        );
+        return $connection->fetchOne($select);
+    }
 }