algorithm - Shopping cart and different kinds of discounts. Storing discounts in DB and applying it to order calculations -

currently, i'm looking best practice "applying discounts" cart/order. so, i'm planning implement such kind of discounts as...

• fixed user's discount (for example, i'd give 10% discount favourite customer)

• discount number of items (for example, you're buying 10 different colored pens , you'll getting discount of 1.5%)

• discount coupon (for example, during promo action we've produced 100 coupons 10% discount each. coupons work 1 order , expire on yyyy-mm-dd)

• present purchasing item or group of items (for example, you're buying pen, list of paper , shop presents sharpener you)

• discount total order price (for example, you're buying 10 pens , gettin no discount, you're adding 5 more pens , getting 5% discount)

only 1 discount applied specific item. we're applying biggest discount. profitable discount user.

beside admin should able modify items price in specific order , cancel discounts in order.

frankly speaking, first ecommerce application , seems me pretty hard task implement these kinds of disounts.

ok, let me tell how i'm going implement...

• fixed user's discount field in users table contains information discount. being set manually through control panel or automatically cron uses having total order summ on n.

• discount number of items i'm going create additional table storing items' groups of such discounts. i'll need 1 more table connect groups items in shop.

• discount coupon table coupons containing field expire day, status of coupon, coupon discount , maybe user_id (owner of coupon). implement coupons categories of items.

• present purchasing item or group of items real pain in ass , totally don't know how implement. please help!

• discount total order price pretty easy, imho.

ok, looking best practices of storing kinds of discounts in db. i'm looking oop practices applying discounts cart. appreciated!

ps: sorry such long post, think interesting not me.

thank you.

a basic solution present purchasing item or group of items requirement have bundle , bundleitem table.

bundle table. id                     int   primary key giftproductid          int   foreign key - product table  bundleitem table. id                     int   primary key bundleid               int   foreign key - bundle table requiredproductid      int   foreign key - product table 

your bundle table contains gift item id , bundleitem table holds items associated bundle user must order qualify gift.

your 'bundle' class contain array of these required product items, gift item , method takes shopping cart object , checks see whether cart contains every required product particular bundle offer - simple foreach within foreach loop...

this simple solution things can complex depending on rules these gift items e.g. if order 2 pens , 2 lists of paper 2 sharpeners? - luck it!