Dynamics 365 - DataSource Method:

public class InventLocation_Extension
{
    ///

    /// Post event handler for InventLocation SalesLine Initialized event.
    ///

    ///
    ///

[FormDataSourceEventHandler(formDataSourceStr(InventLocation, InventLocation), FormDataSourceEventType::Initialized)]
    public static void InventLocation_OnInitialized(FormDataSource sender, FormDataSourceEventArgs e)
    {
        InventLocation  inventLocation = sender.cursor();
        if (inventLocation.InventLocationId)
    {
        info("There is inventLocation Id existed");
    }
    else
    {
        info("There is NO inventLocation Id");
    }
    }
}