使用任何（）返回錯誤VB.NET

Question

檢查行

我有以下功能：

Public Function CheckHasRoom(people_id As String, semester As String, year As String) 
    ' Don't let folks already registered for a room register for another. 
    Dim RoomSelected As String 
    Using dbContext As pbu_housingEntities = New pbu_housingEntities 
     Dim hasroom = (From p In dbContext.Residents _ 
         Where p.people_code_id = people_id _ 
         Where p.semester = semester _ 
         Where p.year = year _ 
         Where (p.room = "" _ 
         Or p.building Is Nothing) _ 
         Select p) 
     If hasroom.Any() Then 
      ' Let them keep going. 
      RoomSelected = "N" 
     Else 
      ' Redirect them to the main page. 
      RoomSelected = "Y" 
      ' HttpContext.Current.Response.Redirect("default.aspx") 
     End If 
    End Using 
    Return RoomSelected 
End Function 

但它在hasroom.Any（）竊聽出來說：「輸入字符串的不正確格式。」任何想法爲什麼？這是返回的行集合，就像我在其他地方使用相同的代碼而沒有問題？

Answer 1

由於DaveMackay建議在他的評論就我看來像WHERE子句中的一個導致錯誤。在代碼的.Any（）點出現錯誤的原因是，這是查詢實際執行的位置，直到您聲明瞭查詢的意圖，但實際上還沒有發生。如果將查詢包裝在括號中並添加.ToList（）結尾，則可能會在聲明查詢的行上發生en錯誤，因爲這會強制立即執行。

從你得到的錯誤我猜這是p.room =「」這是做的，是p.room一個字符串值？如果不是那麼檢查所有其他的子句，它們都是字符串嗎？那年我看起來不太可能，尤其是將它存儲爲一個字符串。

Answer 2

.Count中嘗試查詢，而不是嘗試使用

Dim hasroom = (From p In dbContext.Residents _ 
        Where p.people_code_id = people_id _ 
        AndAlso p.semester = semester _ 
        AndAlso p.year = year _ 
        AndAlso (p.room = "" _ 
        Or p.building Is Nothing) _ 
        Select p).count 

'-------- Example -------- 

Public Sub test() 

    Dim l1 As New List(Of String) From {"1", "2", "3"} 
    Dim l2 As New List(Of String) From {"1", "2", "3", "4", "5"} 

    'return nothing 
    Dim noresult = From p In l1 Where 1 = 0 Select p 

    'return ienumerable 
    Dim someresult = From p In l1 Where p > 2 Select p 

    'return ienumerable with count = 1 with handled_noresult(0)=Nothing 
    Dim handled_noresult = (From p In l1 Where 1 = 0 Select p).DefaultIfEmpty 

    'return emtpty array with .Length=0 --try this 
    Dim handled_noresult2 = (From p In l1 Where 1 = 0 Select p).ToArray 

    'return 1 
    Dim FakeNoResult1 = handled_noresult.Count() 

    'return 0 
    Dim FakeNoResult2 = handled_noresult2.Count() 

End Sub 

Answer 3

p.room = '' 

p.room = ""