Question

如何使用LINQ或HQL执行以下SQL查询？

SELECT `year`, `month`, COUNT(code_id) 
  FROM (SELECT DISTINCT request_codes_id AS code_id, 
    YEAR(requested) AS `year`, MONTH(requested) AS `month` FROM requests) r
  GROUP BY `year`, `month`
  ORDER BY `year`, `month`;

我尝试了以下内容：

var items = from r in TestaccountRequest.Queryable
            group r by r.RequestCodeId into g
            select g.First();
var grouped = from r in items
                group r by r.Requested.ToString("yyyyMM") into y
                select new { Year = y.First().Requested.Year, Month = y.First().Requested.Month, Count = y.Count() };

投了一个System.String ToString(System.String) NotSupportedException。

更新

第一个LINQ-Query中的g.First()似乎会导致问题，因为如果我只运行第一个问题，我会得到一个Code supposed to be unreachable - 例外，但如果我删除了.First()它“有效”，但不会返回我需要的东西。

Answer 1

按匿名类型分组：

var grouped = from r in items
              group r by new { Year = r.Requested.Year,
                               Month = r.Requested.Month } into g 
              select new { g.Key.Year, g.Key.Month, Count = g.Count() };

Answer 2

我有点用以下方法解决了它：

var items = from r in TestaccountRequest.Queryable
            group r by r.RequestCodeId into g
            select g.ElementAt(0);
var grouped = from r in items.ToList()
              group r by new { Year = r.Requested.Year,
                               Month = r.Requested.Month } into g 
              select new { g.Key.Year, g.Key.Month, Count = g.Count() };

但我认为这不是最佳解决方案，因为所有对象都是从数据库中获取的，但至少它现在正在运行，但如果可用，请提供更好的解决方案。

修改
我现在用HQL解决了它：

HqlBasedQuery query = new HqlBasedQuery(typeof(ActivationCodeTestaccountRequestRecord), "SELECT DISTINCT r.ActivationCodeId, YEAR(r.Requested), MONTH(r.Requested) " + "FROM ActivationCodeTestaccountRequestRecord r"); var items = from object[] row in (ArrayList)ActiveRecordMediator.ExecuteQuery(query) group row by new { Year = row[1], Month =row[2] } into g2 select new { Year = g2.Key.Year, Month = g2.Key.Month, Count = g2.Count() };

如何区分选择和分组城堡活动记录？

2 个答案: