試圖查詢數據庫

Question

我有一個問題填充集合類與數據庫中的值。每次循環訪問WHILE DR.READ循環中的記錄時，最後一個記錄將寫入集合中的所有其他項目。我的returnVal集合有幾個相同的項目，儘管循環顯示每個單獨的記錄被添加到returnVal中。謝謝你的幫助。

Public Shared Function getStuff(ByVal sb As StringBuilder) As System.Collections.Generic.List(Of Minutes) 

    Dim returnVal As New System.Collections.Generic.List(Of Minutes) 

    Dim conn As New SqlConnection 

    Dim cmd As New SqlCommand 

    Dim dr As SqlDataReader 

    conn.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings("ConnectionString").ConnectionString 
    cmd.Connection = conn 
    cmd.CommandText = sb.ToString 

    Try 
     conn.Open() 
     dr = cmd.ExecuteReader 

     While dr.Read 
      Dim _minutes As New Minutes 
      _minutes.Minutes = dr("minutes") 
      _minutes.MinutesId = dr("minutesId") 
      returnVal.Add(_minutes) 
     End While 


    Catch ex As Exception 
     Dim _minutes As New Minutes 
     _minutes.Minutes = ex.ToString 
     _minutes.MinutesId = 0 
     returnVal.Add(_minutes) 
    End Try 
    conn.Close() 
    Return returnVal 

End Function 

這是我的分鐘級

Imports Microsoft.VisualBasic 

Public Class Minutes 

    Private Shared _minutesId As Integer 

    Private Shared _minutes As String 


    Public Property MinutesId() As Integer 
     Get 
      Return _minutesId 
     End Get 
     Set(ByVal value As Integer) 
      _minutesId = value 
     End Set 
    End Property 
    Public Property Minutes() As String 
     Get 
      Return _minutes 
     End Get 
     Set(ByVal value As String) 
      _minutes = value 
     End Set 
    End Property 
    Public Shared Function getStuff(ByVal sb As StringBuilder) As System.Collections.Generic.List(Of Minutes) 
     Return MinutesDA.getStuff(sb) 
    End Function 
    Public Shared Function modify(ByVal sb As StringBuilder) As String 
     Return MinutesDA.modify(sb) 
    End Function 
    Public Shared Property Id() As Integer 
     Get 
      Return MinutesDA.Id 
     End Get 
     Set(ByVal value As Integer) 
      MinutesDA.Id = value 
     End Set 
    End Property 
    Public Shared Property Index() As Integer 
     Get 
      Return MinutesDA.Index 
     End Get 
     Set(ByVal value As Integer) 
      MinutesDA.Index = value 
     End Set 
    End Property 
End Class 

Answer 1

問題在於Minutes類中的字段是共享的。將有一個該類的所有實例共享的字段實例。從田地移除「共享」：

Private _minutesId As Integer 

Private _minutes As String 

這將存儲值對每個實例分別

Answer 2

要確認你得到新的值或相同的值試試這個：

Dim i as Integer 
    i = 0 
    While dr.Read 

     Dim _minutes As New Minutes 
     _minutes.Minutes = dr("minutes") 
     ' _minutes.MinutesId = dr("minutesId") 
     _minutes.MinutesId = i 
     i = i + 1 
     returnVal.Add(_minutes) 
    End While 

此之後，你可以看到，如果MinuteId是不同的。

N.B.在VB6中，您必須在循環結束時將_minutes設置爲Nothing來獲取新實例。但是我不會認爲VB.NET中會出現這種情況。