不从数据库中删除

Question

我的代码没有从数据库中删除任何行。这些行显示在表单的列表视图中。它们可以从表单的列表视图中删除和消失，但不会从数据库表中删除。

另外，我使用 MS Access 作为数据库。

这是代码

 Public Sub DeleteProduct()

        If ListView1.SelectedIndices.Count <= 0 Then
            Return
        End If

        Dim ItemNo As Integer = ListView1.SelectedIndices(0)
        Try
            Dim I As Integer = MsgBox("Are you sure you want to delete this record? You can't Undo", MsgBoxStyle.YesNo, "Are you sure?")
            If I = MsgBoxResult.Yes Then
                conn.Open()
                Dim cmd2 As New OleDb.OleDbCommand("DELETE FROM PRODUCT WHERE product_id = '" & ListView1.Items(ItemNo).SubItems(0).Text & "'", conn)
                cmd2.ExecuteNonQuery()
                MsgBox("Record removed successfully", MsgBoxStyle.OkOnly, "Remove Succeeded")
            Else
                Return
            End If
        Catch ex As Exception
            MsgBox(ex.Message)
        Finally
            conn.Close()
        End Try
        Refresh()

    End Sub

Answer 1

将用户界面代码与数据库代码分开。

连接和命令需要调用 Dispose 方法，因此它们应该在 Using 块中本地声明。养成使用Parameters而不是连接字符串来构建sql语句的习惯。

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    If ListView1.SelectedIndices.Count = 0 Then
        MessageBox.Show("You must select an item to delete.")
        Exit Sub
    End If
    If MessageBox.Show("Are you sure you want to delete this record? You can't Undo", "Are you sure?", MessageBoxButtons.YesNo) = DialogResult.Yes Then
        Dim ItemNo As Integer = ListView1.SelectedIndices(0)
        Dim ProductID = CInt(ListView1.Items(ItemNo).Text)
        Dim RecordsDeleted As Integer
        Try
            RecordsDeleted = DeleteProduct(ProductID)
        Catch ex As Exception
            MsgBox(ex.Message)
            Exit Sub
        End Try
        If RecordsDeleted = 1 Then
            MessageBox.Show("Record removed successfully", "Remove Succeeded")
            ListView1.Items.RemoveAt(ItemNo)
        Else
            MessageBox.Show("Record was not deleter")
        End If
    End If
End Sub

Private OPConStr As String = "Your connection string."

Public Function DeleteProduct(ID As Integer) As Integer
    Dim retval As Integer
    Using conn As New OleDbConnection(OPConStr),
            cmd As New OleDbCommand("DELETE FROM PRODUCT WHERE product_id = @ID", conn)
        cmd.Parameters.Add("@ID", OleDbType.Integer).Value = ID
        conn.Open()
        retval = cmd.ExecuteNonQuery
    End Using
    Return retval
End Function