public Purchase(DateTime purchaseTime, BookDetails bookDetails, int numberOfBooks)
{
PurchaseTime = purchaseTime;
BookDetails = bookDetails;
NumberOfBooks = numberOfBooks;
}
public BuyBook(Publisher publisher, BookDetails bookDetails, DateTime purchaseTime, int numberOfBooks)
: base(purchaseTime, bookDetails, numberOfBooks)
{
Publisher = publisher;
bookDetails.Count += numberOfBooks;
}