@RequiresSession
  public ExtensionLinkEntity findById(long linkId) {
    return entityManagerProvider.get().find(ExtensionLinkEntity.class, linkId);
  }
Gets an extension link with the specified ID.

@param linkId
         the ID of the extension link to retrieve.
@return the extension or {@code null} if none exists.
ambari-server/src/main/java/org/apache/ambari/server/orm/dao/ExtensionLinkDAO.java