class TotalProductSalesByCountry(ReportView):
    report_title = _("Product Sales by Country")
    report_description = _("Group by using Django's double-underscore traversal (group_by='client__country').")

    report_model = SalesTransaction
    date_field = "date"
    group_by = "client__country"  # notice the double underscore
    columns = [
        "client__country",
        ComputationField.create(Sum, "value", name="sum__value", verbose_name="Total Value sold by country $"),
    ]

    chart_settings = [
        Chart(
            "Total sold by country $",
            Chart.PIE,  # A Pie Chart
            data_source=["sum__value"],
            title_source=["client__country"],
        ),
    ]