给定:
a chunk of books and each book will associated with unique id
场景:
user can order more than one book
目标:
making an NSMutableURLRequest and send this request to server and let server know which books
are being picked
问题:
For example, user A will choose 3 books whose id are a, b ,c. How can I send an array
containing with these id in the request so that server can know that user A are ordering these books