Question

我遇到了让NHibernate执行分页结果分组的问题。我正在尝试从一组数据中获取，在日期范围内获取数据，通过SearchTerm列对过滤的数据组进行分组，并选择具有最新SearchDate的行。所有这些都在分页数据时。

var results = _nHibernateSession.Query<SearchLog>()
    .Where(x => x.SearchDate <= DateTime.Now && x.SearchDate >= DateTime.Now.AddDays(-30))
    .GroupBy(x => x.SearchTerm)
    .Select(g => g.OrderBy(x => x.SearchDate).FirstOrDefault())
    .Skip((page - 1) * pageSize)
    .Take(pageSize)
    .ToList;

var count = _nHibernateSession.Query<SearchLog>()
    .Where(x => x.SearchDate <= DateTime.Now && x.SearchDate >= DateTime.Now.AddDays(-30))
    .GroupBy(x => x.SearchTerm)
    .Select(g => g.OrderBy(x => x.SearchDate).FirstOrDefault())
    .Count();

var results = query.ToList();

生成的查询是

SELECT TOP (20 /* @p0 */) 
       * /* Replacing selects here with star to reduce lines */
FROM   (select search0_.search_id                            as search1_51_,
               search0_.search_term                          as search7_51_,
               search0_.search_date                          as search9_51_
               ROW_NUMBER() OVER(ORDER BY CURRENT_TIMESTAMP) as __hibernate_sort_row
        from   SearchLog.dbo.SearchLog search0_
        where  search0_.search_dt <= '2017-04-12T11:29:57' /* @p1 */
           and search0_.search_dt >= '2017-03-13T11:29:57' /* @p2 */
        group  by search0_.search_term) as query
WHERE  query.__hibernate_sort_row > 0 /* @p3 */
ORDER  BY query.__hibernate_sort_row

正如您所看到的，它没有生成要按其他行分组的SQL，而只是按SearchTerm进行分组，这会抛出错误，说明“某些列在选择列表中无效，因为它不包含在聚合函数中或者GROUP BY子句“。

NHibernate版本： 3.3.3.4001

这是我正在寻找的但是有分页（Skip，Take）

SELECT s.*
FROM SearchLog.dbo.SearchLog s
INNER JOIN (SELECT   MAX(id) AS MaxSearchId,
                     search_term
            FROM     SearchLog.dbo.SearchLog
            WHERE    user_id = '123'
              AND    search_dt <= '2017-04-12T12:09:50'
              AND    search_dt >= '2017-03-13T12:09:50'
            GROUP BY search_term) groupeds
ON s.id = groupeds.MaxSearchId
ORDER BY s.search_dt DESC

值得注意的是，我想计算结果的数量，这也是由group by子句产生的。但是，我不知道如何用这个做一个未来，这样我就可以进行1次DB往返而不是2次，无论如何都可以使这个查询更有效率。

更新这是我尝试的东西，但似乎仍无法使其正常工作

var distinctQuery =
(
    from ds in _nHibernateSession.Query<SearchLog>()
    where ds.UserId == userId.ToString() && ds.SearchDate <= DateTime.Now && ds.SearchDate >= DateTime.Now.AddDays(-30)
    group ds by ds.SearchTerm into g
    select new { NumericalId = g.Max(s => s.NumericalId), SearchTerm = g.Key, SearchDate = g.Max(s => s.SearchDate) }
);

var result = 
(
    from s in _nHibernateSession.Query<SearchLog>()
    join ds in distinctQuery on s.NumericalId equals ds.NumericalId
    select s
).ToArray();

我收到错误消息“不支持指定方法”。我只是想做一些不可能的事情吗？

NHibernate从分组中获取最大日期

0 个答案: