Ecommerce - MongoDB Applied Design Patterns - page 109

update = { '$set' : { 'status' : 'pending' , 'last_modified' : now } } )
iif not not result [ 'updatedExisting' ]:

raise raise CartInactive ()

try try :

collect_payment ( cart )
except except :

db . cart . update (
{ '_id' : cart_id },
{ '$set' : { 'status' : 'active' } } )
raise

raise
db . cart . update (
{ '_id' : cart_id },
{ '$set' : { 'status' : 'complete' } } )
db . product . update (
{ 'carted.cart_id' : cart_id },
{ '$pull' : { 'cart_id' : cart_id } },
multi = True )

We're using the return value from update here to let us know whether we actually
locked a currently active cart by moving it to pending status.

We're using multi=True here to ensure that all the SKUs that were in the cart have
their carted properties updated.

Here, we could actually use a new index on the carted.cart_id property so that our final
update is fast:

>>> >>> db . product . ensure_index ( 'carted.cart_id' )

Returning inventory from timed-out carts

Periodically, we need to “expire” inactive carts and return their items to available inventory.
Our approach here is as follows:

1. Find all carts that are older than the threshold and are due for expiration. Lock them
by setting their status to "expiring" .

2. For each "expiring" cart, return all their items to available inventory.

3. Once the product collection has been updated, set the cart's status to "expired" .