從Linq到SQL查詢的自定義日期格式

Question

使用folowing函數返回一個SelectList。我需要在Descr上的自定義格式，但將Key.ToString（）替換爲Key.ToString（「DD/MM/YY」）會給我提供錯誤「Method」System.String ToString（System.String）' SQL。「我如何在Descr上使用自定義日期格式？

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

如果你把轉換放在LINQ to SQL查詢中，它會嘗試從它創建一個SQL查詢。首先獲取結果，將其實現爲日期列表，然後使用LINQ to Objects進行轉換。

我覺得是這樣的：

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