I have a Purchas use case, where customers will purchase certain items in an application. Several users might do this at the same time. We have a database table that maintain count of these items and item name etc.

I am thinking of using a QP to which the purchase will be queued upon submit.

IN the QP activity, first a check if made for availbility, if count of available items >0 the count is altered and purchase is allowed to make. If not, an error needs to be returned to user.

My question is how can I return this error to the user, without having a case type. Is having a case type must. If so, do I need to have the case go to wait shape while the success/failure comes.

This doesn't look good from end user perspective when all they are trying to do is make a simple purchase.