<dx:BootstrapGridView runat="server" DataSourceID="CustomersDataSource" KeyFieldName="CustomerID">
    <SettingsDetail ShowDetailRow="true" />
    <Columns>
        <dx:BootstrapGridViewDataColumn FieldName="ContactName" />
        <dx:BootstrapGridViewDataColumn FieldName="CompanyName" />
        <dx:BootstrapGridViewDataColumn FieldName="City" />
        <dx:BootstrapGridViewDataColumn FieldName="Country" />
    </Columns>
    <Templates>
        <DetailRow>
            <dx:BootstrapGridView runat="server" DataSourceID="InvoicesDataSource" KeyFieldName="OrderID;ProductID"
                OnBeforePerformDataSelect="detailGrid_DataSelect" OnCustomUnboundColumnData="detailGrid_CustomUnboundColumnData">
                <Columns>
                    <dx:BootstrapGridViewDataColumn FieldName="OrderID" Caption="Order ID" />
                    <dx:BootstrapGridViewDataColumn FieldName="OrderDate" />
                    <dx:BootstrapGridViewDataColumn FieldName="ShipName" />
                    <dx:BootstrapGridViewTextColumn FieldName="UnitPrice">
                        <PropertiesTextEdit DisplayFormatString="c" />
                    </dx:BootstrapGridViewTextColumn>
                    <dx:BootstrapGridViewDataColumn FieldName="Quantity" Name="Quantity" />
                    <dx:BootstrapGridViewTextColumn FieldName="Total" UnboundType="Decimal">
                        <PropertiesTextEdit DisplayFormatString="c" />
                    </dx:BootstrapGridViewTextColumn>
                </Columns>
                <SettingsPager PageSize="5"></SettingsPager>
            </dx:BootstrapGridView>
        </DetailRow>
    </Templates>
</dx:BootstrapGridView>
<ef:EntityDataSource runat="server" ID="CustomersDataSource" ContextTypeName="DevExpress.Web.Demos.NorthwindContextSL" EntitySetName="Customers" />
<ef:EntityDataSource runat="server" ID="InvoicesDataSource" ContextTypeName="DevExpress.Web.Demos.NorthwindContextSL" EntitySetName="Invoices" Where="it.CustomerID = @CustomerID">
    <WhereParameters>
        <asp:SessionParameter Name="CustomerID" SessionField="CustomerID" Type="String" />
    </WhereParameters>
</ef:EntityDataSource>

protected void detailGrid_DataSelect(object sender, EventArgs e) {
    Session["CustomerID"] = (sender as BootstrapGridView).GetMasterRowKeyValue();
}
protected void detailGrid_CustomUnboundColumnData(object sender, ASPxGridViewColumnDataEventArgs e) {
    if(e.Column.FieldName == "Total") {
        decimal price = (decimal)e.GetListSourceFieldValue("UnitPrice");
        int quantity = Convert.ToInt32(e.GetListSourceFieldValue("Quantity"));
        e.Value = price * quantity;
    }
}