在LINQ查詢中調用用戶定義的函數

Question

我在網上看到過有關此的幾頁，但不幸的是示例代碼是用C＃編寫的。我無法理解它的大部分內容（和/或通過代碼翻譯器運行它），但我仍然需要幫助使其在VB中工作。

我的自定義函數是：

Public Shared Function GetFriendlyTitle(Title As String) As String 
    Dim ConvertedTitle As String = "" 
    Try 
     Dim oRE As Regex = New Regex("[^a-zA-Z0-9\s]") 
     ConvertedTitle = Trim(oRE.Replace(Title, "")).Replace(" ", "_") 
    Catch ex As Exception 
     LogError(ex) 
    End Try 
    Return ConvertedTitle 
End Function 

，這裏是我打電話回產品的功能：

Public Shared Function GetProductByTypeAndTitle(URLFriendlyTitle As String, ProductType As ProductType) 
    Try 
     'don't know why, but the server threw errors if I went c.Type=Type 
     Dim pt As Integer = CInt([Enum].Parse(GetType(ProductType), [Enum].GetName(GetType(ProductType), ProductType))) 

     Dim context As LionsSharePressEntities = New LionsSharePressModel.LionsSharePressEntities 
     return From p In context.Products Where GetFriendlyTitle(p.Title) = URLFriendlyTitle AndAlso p.Type = pt 
    Catch ex As Exception 
     LogError(ex) 
     Return nothing 
    End Try 
End Function 

它編譯罰款，但是當我運行它掛起。這就是那個迴歸線。

Answer 1

嘗試添加Select聲明：

return From p In context.Products 
      Where GetFriendlyTitle(p.Title) = URLFriendlyTitle 
      AndAlso p.Type = pt 
      Select p 

Answer 2

你讀這篇文章的MSDN？

http://msdn.microsoft.com/en-us/library/bb399416%28v=vs.90%29.aspx?cs-save-lang=1&cs-lang=vb#code-snippet-2

Answer 3

這個問題是有點老了，並似乎已經得到了解決。但是我仍然在發佈這個消息，希望這可能會幫助別人解決問題，併爲我解決問題。

另外請注意，我不能讓我的函數從w /在我的LINQ查詢「Shared」中調用，這使我的情況稍有不同。我認爲更有理由發佈其他答案。

Public Function GetFriendlyTitle(Title As String) As String 
    Dim ConvertedTitle As String = "" 
    Try 
     Dim oRE As Regex = New Regex("[^a-zA-Z0-9\s]") 
     ConvertedTitle = Trim(oRE.Replace(Title, "")).Replace(" ", "_") 
    Catch ex As Exception 
     LogError(ex) 
    End Try 
    Return ConvertedTitle 
End Function 

當我遇到了一個問題呼叫從瓦特/在LINQ查詢這個非共享用戶定義函數是我如何解決其使用的OP代碼段，例如，

Public Shared Function GetProductByTypeAndTitle(URLFriendlyTitle As String, _ 
               ProductType As ProductType) 
    Try 
     'don't know why, but the server threw errors if I went c.Type=Type 
     Dim pt As Integer = _ 
       CInt([Enum].Parse(GetType(ProductType), _ 
        [Enum].GetName(GetType(ProductType), ProductType))) 
     Dim context As New LionsSharePressModel.LionsSharePressEntities 

     '// Here is the lambda that will call your GetFriendlyTitle function 
     Dim callUserFunc As Func(Of String, String) = _ 
       Function(title As String) 
        Return GetFriendlyTitle(title) 
       End Function 

     '// Now call Invoke on the lambda and pass in the needed param(s) from within your LINQ query 
     return From p In context.Products _ 
       Where callUserFunc.Invoke(p.Title) = URLFriendlyTitle AndAlso p.Type = pt 

     '//return From p In context.Products Where GetFriendlyTitle(p.Title) = URLFriendlyTitle AndAlso p.Type = pt 

    Catch ex As Exception 

     LogError(ex) 
     Return nothing 

    End Try 
End Function