[英]How to handle DBNull? VB.NET
I have form that has datagrid and some textbox controls. 我有具有datagrid和一些文本框控件的窗体。 Basically, Im performing Add function. 基本上,我执行添加功能。 Whenever I add, it scans the maximum value and it will increment by one. 每当我添加时,它都会扫描最大值,并且将增加一。 I only designed for auto increment. 我只为自动递增而设计。 My problem is, how can I increment when the ExecuteScalar gets a null value. 我的问题是,当ExecuteScalar获得空值时,如何递增。 Here's the sample codes 这是示例代码
Public Sub IncrementID()
conn = New MySqlConnection
conn.ConnectionString = "server=localhost; userid=root; password=root; database=uecp_cens"
Try
conn.Open()
Dim insert_coupon_query As String = ("SELECT MAX(faculty_ID) from uecp_cens.tblfacultyinfo")
Dim cmd_query As New MySqlCommand(insert_coupon_query, conn)
Dim cmd_result As Integer = CInt(cmd_query.ExecuteScalar()) 'THIS IS WHERE THE ERROR OCCURS, IT GIVES ME 'InvalidCastException was unhandled' Conversion from type 'DBNull' to type 'Integer' is not valid.
txtFacultyNo.Text = cmd_result + 1
Catch ex As MySqlException
MessageBox.Show(ex.Message)
Finally
conn.Dispose()
End Try
End Sub
Any help is appreciated. 任何帮助表示赞赏。
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you should write this casting 你应该写这个演员表
cmd.CommandText = "SELECT COUNT(*) FROM dbo.region";
Int32 count = (Int32) cmd.ExecuteScalar();
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