Question

我正在处理由datagridview组成的客户数据库和vb.net表单。

我包括3列：

customer_id, customer_name, customer_Notes

我创建了两个功能来简化我的工作，一个功能用于将数据从datagridview插入到MS Access数据库中，另一个功能用于更新datagridview中显示的数据。

嗯，我遇到了问题。我收到有关从'DBNull'类型到'string'类型转换的错误消息。

无论我是插入还是更新以下列之一，如果都无法填充datagridview列中的至少一列，则会出现错误消息：

customer_id, customer_name, customer_Notes

否则一切都很好。

在我在这里提出问题之前，我已经在网上搜索过，并且我知道我将首先测试DBNull，但是我没有学会正确的方法。

插入功能：

 Public Sub insert_customer(ByVal customer_id As Integer, ByVal customer_name As String, ByVal customer_address As String, ByVal customer_phone As String, ByVal customer_notes As String)
        Try
            Dim cmd As New OleDbCommand("insert into tblCustomers (CustomerID , CustomerName , CustomerNotes) values (@CustomerID,@CustomerName ,  @CustomerNotes) ", conn_Access)

            cmd.Parameters.Add("@CustomerID", OleDbType.Integer).Value = customer_id
            cmd.Parameters.Add("@CustomerName", OleDbType.VarWChar).Value = customer_name

            cmd.Parameters.Add("@CustomerNotes", OleDbType.VarChar).Value = customer_notes

            conn_Access.Open()
            cmd.ExecuteNonQuery()
            conn_Access.Close()
            cmd = Nothing
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
  End Sub

更新功能：

 Public Sub update_customer(ByVal customer_name As String, ByVal customer_notes As String, ByVal Customer_ID2 As Integer)
        Try
            Dim cmd As New OleDbCommand("update  tblCustomers set CustomerName= @CustomerName , CustomerNotes= @CustomerNotes where CustomerID = @CustomerID2 ", conn_Access)

            cmd.Parameters.Add("@CustomerName", OleDbType.VarChar).Value = customer_name

            cmd.Parameters.Add("@CustomerNotes", OleDbType.VarChar).Value = customer_notes
            cmd.Parameters.Add("@CustomerID2", OleDbType.Integer).Value = Customer_ID2

            conn_Access.Open()
            cmd.ExecuteNonQuery()
            conn_Access.Close()

            cmd = Nothing

        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try

  End Sub

私有子Btn_save_Click（ByVal发送者作为System.Object，ByVal e作为System.EventArgs）处理Btn_save.Click '更新 'اولعمود 试试

        For i As Integer = 0 To DataGridView1.Rows.Count - 2

            With DataGridView1.Rows(i)
                'اول عمود 

                If count_customer_id_from_customers(.Cells(0).Value) = 1 Then
                    'update

                    update_customer(.Cells(1).Value, .Cells(2).Value, .Cells(3).Value, .Cells(4).Value, .Cells(0).Value)

                Else
                    'insert
                    insert_customer(.Cells(0).Value, .Cells(1).Value, .Cells(2).Value, .Cells(3).Value, .Cells(4).Value)
                End If
            End With
        Next

load_Customers（）

    Catch ex As Exception
        MessageBox.Show(ex.Message)
    End Try


End Sub

任何帮助将不胜感激

预先感谢

Visual Basic 2010数据库中的DBNull异常

0 个答案: