如何将购物车数据的 session 信息添加到数据库中？

Question

i have a shopping cart and i wanted to store the shopping cart information to my database but i have no idea how to do it since i have no way to detect how many items my customer would add to their shopping cart.

What i have in mind right now would be having a non-unique key as shopping cart id. IE

ID / book / price / quantity
1/harry potter/19.90/1
1/deadly hollows/49.90/1

and both of id 1 will consitute as a complete shopping cart. Will there be something wrong with this way of doing?

Answer 1

You should have a Primary Key that is unique, but can span multiple columns:

You could probably use ID and book as your Primary Key, since each cart won't have 2 copies of the same book, because that would just update the quantity, not add a new row.

Answer 2

A non-unique key is not a good solution.
I would add an auto-increment key to the shopping cart table and use that as "real" unique key.
Just keep your non-unique ID as it is, so you can use it as an OrderID to see which rows belong to the same order.

Like this:

UniqueID / OrderID / book / price / quantity
1/1/harry potter/19.90/1
2/1/deadly hollows/49.90/1
3/2/code complete/25.90/2