Question

我的程序无法自动计算我的ID。我缺少一些东西。有人可以帮我看看

Private Sub getNextNumber()
        If Not app.State = ConnectionState.Open Then
            'open connection
            app.Open()
        End If

        Dim da As New OleDb.OleDbDataAdapter("select top 1 ID from ADMIN order by ID desc;", app)
        Dim dt As New DataTable
        'fill data to datatable
        da.Fill(dt)
        app.Close()

        If dt.Rows.Count > 0 Then
            txtID.Text = (Val(dt.Rows(0)(0)) + 1).ToString.PadLeft(10, "B")
        Else
            txtID.Text = "1".PadLeft(10, "B")
        End If
    End Sub

Private Function getLastNumber() As Integer
    Dim app1 As New OleDb.OleDbConnection
    app1.ConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=MYX.accdb"
    If Not app1.State = ConnectionState.Open Then
        app1.Open()
    End If

    Dim da As New OleDb.OleDbDataAdapter("select top 1 ID from ADMIN order by ID desc;", app1)
    'desc = sort the data returned in descending order
    Dim dt As New DataTable

    da.Fill(dt)
    app1.Close()

    If dt.Rows.Count > 0 Then
        Return Val(dt.Rows(0)(0))
    End If
    Return 0
End Function

我在这一部分是否编码错误？

If dt.Rows.Count > 0 Then
          txtID.Text = (Val(dt.Rows(0)(0)) + 1).ToString.PadLeft(10, "B")
      Else
          txtID.Text = "1".PadLeft(10, "B")
      End If

Answer 1

Using...End Using块将关闭并处置您的数据库对象，即使发生错误也是如此。在本地创建连接时，无需检查连接状态。

将连接字符串直接传递给连接的构造函数。同样，将sql语句和连接直接传递给命令的构造函数。您不需要DataAdapter或DataTable。

.ExecuteScalar返回一个对象（结果集的第一行，第一列），因此我们在Using块外声明一个Object变量，以便在关闭连接后可以使用它。我们可以使用.ExecuteScalar，因为您只返回1行，而该行仅返回一列。

接下来，在正确关闭并处置连接和命令后，我们检查retVal是否为Nothing，如果为Private conString As String = "Provider=Microsoft.ACE.OLEDB.12.0; Data Source=MYX.accdb" Private Function getLastNumber() As Integer Dim retVal As Object Using app1 As New OleDb.OleDbConnection(conString) Using cmd As New OleDbCommand("select top 1 ID from ADMIN order by ID desc;", app1) app1.Open() retVal = cmd.ExecuteScalar() End Using End Using If retVal Is Nothing Then Return 0 End If Dim arrChar = retVal.ToString.ToCharArray() Dim result = (From c In arrChar Where Char.IsNumber(c) Select c).ToArray Dim num = CInt(String.Join("", result)) Return num End Function，则返回0。

如果未通过测试，则更改为Char数组。使用Linq提取数组的数字。最后，将其连接为一个字符串并转换为数字。

Private Sub GetNextID()
    Dim retVal As Object
    Using app As New OleDbConnection(conString)
        Using cmd As New OleDbCommand("select top 1 ID from ADMIN order by ID desc;", app)
            app.Open()
            retVal = cmd.ExecuteScalar
        End Using
    End Using
    If retVal Is Nothing Then
        txtID.Text = "1".PadLeft(10, "B"c)
        Return
    End If
    Dim arrChar As Char() = retVal.ToString.ToCharArray
    Dim result = (From c In arrChar
                  Where Char.IsNumber(c)
                  Select c).ToArray
    Dim num = CInt(String.Join("", result))
    txtID.Text = (num + 1).ToString.PadLeft(10, "B"c)
End Sub

明智的选择您的下属...

{{1}}

我希望这是单个用户，否则这些方法会遇到很大的问题。

自动生成失败的ID

1 个答案: