从Linq到SQL查询的自定义日期格式

Question

使用folowing函数返回一个SelectList。我需要在Descr上的自定义格式，但将Key.ToString（）替换为Key.ToString（“DD/MM/YY”）会给我提供错误“Method”System.String ToString（System.String）' SQL。“我如何在Descr上使用自定义日期格式？

Public Function ReturnDates(ByVal Param_Pesq_Cod As Integer) As SelectList 
     Dim Qry = From E In DB.Execs _ 
     Where E.Pesq_Cod = Param_Pesq_Cod _ 
     Group E By Key = E.DataHora.Date _ 
     Into Group Order By Key Select New With {.Descr = Key.ToString(), .Val = Key} 

     Return New SelectList(Qry, "Val", "Descr") 
    End Function 

Answer 1

如果你把转换放在LINQ to SQL查询中，它会尝试从它创建一个SQL查询。首先获取结果，将其实现为日期列表，然后使用LINQ to Objects进行转换。

我觉得是这样的：

Public Function ReturnDates(ByVal Param_Pesq_Cod As Integer) As SelectList 
    Dim Qry = From E In DB.Execs _ 
    Where E.Pesq_Cod = Param_Pesq_Cod _ 
    Group E By Key = E.DataHora.Date _ 
    Into Group Order By Key Select Key 

    Dim List = _ 
    Qry.ToList() _ 
    .Select(Function(d) New With {.Descr = d.ToString(), .Val = d}) 

    Return New SelectList(List, "Val", "Descr") 
End Function