如果您知道树中只有两个级别，那么您是否考虑过加入更深的一个级别。像下面的东西？
SELECt DISTINCT domain FROM Domain domain LEFT OUTER JOIN FETCH domain.operators operators1 LEFT OUTER JOIN FETCH domain.networkCodes LEFT OUTER JOIN FETCH operators1.operators operators2 LEFT OUTER JOIN FETCH operators1.networkCodesWHERe domain.domainId = :domainId
