Question

我已经在Linqer中尝试了以下LINQ查询它工作正常，但是当我尝试使用C＃时它给出了以下错误

from IHeal_Mnt_Tickets in iHealEntities.iHeal_Mnt_Tickets
    where
        Tickets.Active == 1 &&
        Tickets.MntID == 1 &&
        Tickets.InsertedOn >= fromdate && 
        Mnt_Tickets.InsertedOn <= todate &&
        (new string[] { "Resolved", "Assigned" }).Contains(Tickets.status)
        group Tickets by new {
            Tickets.Instance
        } into g
            select new {
              Instance = g.Key.Summus_Instance,
              Assigned = (Int64?)g.Count(p => p.iHealID != null),
              resolved = (System.Int64?)g.Sum(p => (p.status == "Resolved" ? 1 : 0)),
              domain = (System.Int64?)g.Sum(p => (p.status == "Assigned" ? 1 : 0)),
              iHeal_Closure = (Decimal?)Math.Round((Double)(Double)g.Sum(p => (p.iHeal_Cur_status == "Resolved" ? 1 : 0)) * 1.0 / (Double)g.Count(p => p.iHealID != null) * 100, 2, MidpointRounding.AwayFromZero)
            };

错误是

"LINQ to Entities does not recognize the method 'Double Round(Double, Int32, System.MidpointRounding)' method, and this method cannot be translated into a store expression."

Answer 1

并非BCL中支持的所有内容都在SQL中具有直接等效功能。鉴于这是查询的最后一部分，最简单的方法是编写一个查询，该查询获取所需的所有数据，无需舍入等，然后使用a将数据转换为首选格式本地查询：

var dbQuery = from item in source
              where filter
              select projection;
// The AsEnumerable() part is key here
var localQuery = from item in dbQuery.AsEnumerable()
                 select complicatedTransformation;

有效地使用AsEnumerable()只会更改编译时类型...以便Select使用委托而不是Enumerable.Select使用表达式树Queryable.Select调用(Double)(Double)。

我希望你能够比现在的方法更简单地进行最终转换 - 像double这样的事情真的不是必要的......并且你转换的任何时候从decimal到{{1}}或反之亦然，你应该质疑这是必要的还是可取的...通常更好地坚持二进制文件浮点或十进制浮点数，而不是混合它们。

LINQ to Entities无法识别方法Double Round（Double，Int32，System.MidpointRounding）方法

1 个答案: