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From Ido Ran <ido....@gmail.com>
Subject Yet another transaction
Date Fri, 22 Oct 2010 09:40:05 GMT
Hi,
I know tx question have been asked, but I never got a straight answer. I
will present an example but I'm afraid that example distract us from the
main issue which is "what is the new way of changing data?"

Suppose I have CouchDB in which each document represent item in my
warehouse. Each item has catalog number and quantity.
I have agents who sale my items all over town, each agent has smart phone
and internet access so they can use my great CouchApp :)
One thing is very important - I don't want agent to sale item I don't have
in stock and have all the items a client order.

So one thing is for sure: We can't simply subtract the quantity client order
from the item document because I might dead-lock myself.
Client 1 order item Ax5, Bx3
Client 2 order item Bx3, Ax10
Suppose I have in stock Ax6, Bx3

If I handle the two client order at the same time, first Client1 item A then
Client 2 item B then Client 1 item B then Client 2 item A
I will get to the last update of item A and find I don't have enough in
stock, but there is no good way of rolling it back, let's say the buttery of
the smartphone is dead I now took only half of the order.

I can create a new document which will represent the order itself. It will
have all the client detail as well as each item and quantity. Further I can
create a validation function to allow only order which have all items in
stock. Does it the way to go?
Let's say I took the solution of order document, how do I actually process
the orders and update the quantity of each item?

I hope I made myself clear, I'm not looking to solve this specific problem
but understand how to use CouchDB as non-transactional database.

Thank you,
Ido

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