The INSERT statement conflicted with the FOREIGN KEY constraint "FK_order_detail_material".

With cn
            If .State = ConnectionState.Open Then .Close()
            .ConnectionString = strconn
            .Open()
        End With

        Dim s As String = ""
        If status = "add" Then
            s = "insert into [order](id_order,id_sup,dateorder,total)"
            s &= " values(@id_or,@id_sup,@dateor,@to)"
        Else
            s = "update [order] set total = @to where id_order = @id_or"
        End If

        Dim cm As New SqlCommand
        With cm
            .CommandType = CommandType.Text
            .CommandText = s
            .Connection = cn
            .Parameters.Clear()
            .Parameters.Add("@id_or", SqlDbType.NVarChar, 5).Value = id_order.Text
            .Parameters.Add("@id_sup", SqlDbType.NVarChar, 6).Value = ComboBox1.SelectedValue
            .Parameters.Add("@dateor", SqlDbType.NVarChar, 10).Value = order_date.Text
            .Parameters.Add("@to", SqlDbType.Int).Value = CSng(txttotal.Text)
            'ขั้นที่ 3 รัน
            .ExecuteNonQuery()

        End With

        For i = 0 To ListView1.Items.Count - 1
            Dim s1 As String = ""
            s1 = "insert into [order_detail](id_order,id_material,unitorder,unitrub)"
            s1 &= "values (@id_or,@id_mat,@unor,@unru)"
            Dim cm1 As New SqlCommand
            With cm1
                .CommandType = CommandType.Text
                .CommandText = s1
                .Connection = cn
                .Parameters.Clear()
                .Parameters.Add("@id_or", SqlDbType.NVarChar, 5).Value = id_order.Text
                .Parameters.Add("@id_mat", SqlDbType.NVarChar, 3).Value = ListView1.Items(i).SubItems(2).Text
                .Parameters.Add("@unor", SqlDbType.Int).Value = ListView1.Items(i).SubItems(4).Text
                .Parameters.Add("@unru", SqlDbType.Int).Value = ListView1.Items(i).SubItems(5).Text
                .ExecuteNonQuery()

            End With
        Next

        MessageBox.Show("บันทึกข้อมูลเรียบร้อย")