@RequiresSession
  public AlertDefinitionEntity findById(long definitionId) {
    return entityManagerProvider.get().find(AlertDefinitionEntity.class,
        definitionId);
  }
Gets an alert definition with the specified ID.

@param definitionId
         the ID of the definition to retrieve.
@return the alert definition or {@code null} if none exists.
ambari-server/src/main/java/org/apache/ambari/server/orm/dao/AlertDefinitionDAO.java