SalesOrderService

public class SalesOrderService
{
    // A command should map to this method.
    public void AddProducToSalesOrder(Guid salesOrderId, Guid productId, int quantity)
    {
        using(var work = GetUnitOfWork())
        {
            var order = work.GetById<SalesOrder>(salesOrderId);
            var product = work.GetById<Product>(productId);

            order.AddProduct(productId, quantity);
            product.DecreaseStockCausedBySalesOrderFooBarForgotTheMethodName(salesOrderId);

            work.Accept();
        }
    }
}