QueryDSL - 按别名排序

Question

我正在使用 queryDSL 从数据库中获取一些额外的数据：

public List<Tuple> getUsersWithData (final SomeParam someParam) {
  QUser user = QUser.user;
  QRecord record = QRecord.record;
  JPQLQuery = query = new JPAQuery(getEntityManager());

  NumberPath<Long> cAlias = Expressions.numberPath(Long.class, "cAlias");
  return query.from(user)
       .leftJoin(record).on(record.someParam.eq(someParam))
       .where(user.active.eq(true))
       .groupBy(user)
       .orderBy(cAlias.asc())
       .list(user, record.countDistinct().as(cAlias));
}

尽管它按预期工作，但它会在 SQL 中生成两个 COUNT()：

SELECT
  t0.ID
  t0.NAME
  to.ACTIVE
  COUNT(DISTINCT (t1.ID))
FROM USERS t0 LEFT OUTER JOIN t1 ON (t1.SOME_PARAM_ID = ?)
WHERE t0.ACTIVE = true
GROUP BY t0.ID, to.NAME, t0.ACTIVE
ORDER BY COUNT(DISTINCT (t1.ID))

我想知道是否有可能得到这样的东西：

SELECT
  t0.ID
  t0.NAME
  to.ACTIVE
  COUNT(DISTINCT (t1.ID)) as cAlias
FROM USERS t0 LEFT OUTER JOIN t1 ON (t1.SOME_PARAM_ID = ?)
WHERE t0.ACTIVE = true
GROUP BY t0.ID, to.NAME, t0.ACTIVE
ORDER BY cAlias

我无法从文档中理解这一点，如果可能的话，请给我一些指导。

Answer 1

    QVehicle qVehicle = QVehicle.vehicle;

    NumberPath<Long> aliasQuantity = Expressions.numberPath(Long.class, "quantity");
    final List<QuantityByTypeVO> quantityByTypeVO = new JPAQueryFactory(getEntityManager())
            .select(Projections.constructor(QuantityByTypeVO.class, qVehicle.tipo, qVehicle.count().as(aliasQuantity)))
            .from(qVehicle)
            .groupBy(qVehicle.type)
            .orderBy(aliasQuantity.desc())
            .fetch();

    select 
       vehicleges0_.type as col_0_0_, count(vehicleges0_.pk) as col_1_0_ 
    from vehicle vehicleges0_ 
    group by vehicleges0_.type 
    order by col_1_0_ desc;

我做过类似的事情，但我确实在订购前先数了数。查看查询和生成的选择。

Answer 2

这是 SQL 而不是 queryDSL 施加的限制。 您可以尝试在数据库控制台中运行建议的查询 - 我认为它不会执行，至少不会在每个数据库上执行。 但我不认为这个重复的 COUNT() 真的会产生任何性能开销。