void SalesReceiptTransaction::Execute()
{
    Employee* e = GpayrollDatabase.GetEmployee(itsEmpid);
    if (e) {
        PaymentClassification* pc = e->GetClassification();
        if (CommissionedClassification* cc = dynamic_cast<CommissionedClassification*>(pc)) {
            cc->AddReceipt(new SalesReceipt(itsSaleDate, itsAmount));
        } else
            throw("Tried to add sales receipt to non-commissioned employee");
    } else
        throw("No such employee.");
}