@Transactional
  public ExtensionLinkEntity merge(ExtensionLinkEntity link) {
    return entityManagerProvider.get().merge(link);
  }
Merge the specified extension link with the existing extension link in the database.

@param link
         the extension link to merge (not {@code null}).
@return the updated extension link with merged content (never {@code null}).
ambari-server/src/main/java/org/apache/ambari/server/orm/dao/ExtensionLinkDAO.java