From: Kaspar Schiess <eule@...>
Date: 2004-05-08T05:39:00+09:00
Subject: Re: What is Borges?

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Carl Youngblood wrote:

| Is that always good?  What if it means the users ends up clicking on the
| purchase button twice and we charge their card twice?  I've always
| thought that it was best not to let the user use the back button in
| cases like these (i.e., forward them to the right page, display an error
| indicating that the posted values are stale, or something like that).

Well, this is actually a problem that has been given some thought. And
thus not a problem. In Borges, you would wrap the sequence of your
checkout steps with:

session.isolate do
	show_checkout_step_1
	show_checkout_step_2
	# etc..
end

The effect of this is that you get a UI Transaction that protects your
checkout steps. Once the user enters the transaction, he can 'back' and
'forth' at will withhin the transaction. But once the final button for
checkout is hit, the transaction will be closed and the user can't go
back - all he gets is a redirection to the current page of the application.

I think that declaring the back button as forbidden is a bad idea,
rather make it work the way we expect it to !

There is also a

session.once do
	show_some_unique_timedependent_info
	show_some_other_stuff
end

that permits to step trough the sequence just *once*. You might want to
download and install Borges and run the following script on your machine
for happy testing of these features (and uh admire the nice
implementation we have ;) )

require 'Borges'
require 'Borges/Test'
require 'Borges/WEBrick'

Borges::WEBrickServlet.start

Then make a connection to localhost:7000/borges/test. I am talking about
~ the Once and the Transaction tab (whoa check out the tab control while
your at it).

The documentation at www.tua.ch/ruby is rather bad I fear; I will
hopefully get to write a full introduction that also explains the
concepts a bit more in depth.

- --
kaspar

semantics & semiotics
code manufacture

www.tua.ch/ruby
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