From: Eric Hodel <drbrain@...7.net>
Date: 2004-05-08T01:06:55-07:00
Subject: Re: What is Borges?

--tuYRN1zEaS85jg/Y
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

Kirk Haines (khaines@enigo.com) wrote:

> On Sat, 8 May 2004 05:33:02 +0900, Julian Fitzell wrote
>=20
> >  Seaside=20
> > (and I believe Borges for Ruby implements this piece too) has a=20
> > concept of transactions or isolate blocks.  The way this works is=20
> > that you execute a section of code inside a block.  When that block=20
> > terminates, all the pages in that session get expired.  So in the=20
> > case of a shopping cart, you would likely start an isolate block=20
> > when they begin the payment process and expire all those pages as=20
> > soon as they press "Purchase".
>=20
> Now THAT is a cool idea.  I need to think about how to steal that and=20
> implement it in Iowa to selectively expire pages from the page cache.  Th=
at=20
> would be a useful capability.

Inside Borges' Session class, the guts of the request handler do this:

1) wait for a request
2) when we have a request, pass it to our current filters
3) when the filters are done with the request, do the 'normal'
   processing work.
4) go back to (1)

Transaction is implemented like this:  So long as the transaction is
active, pages within.  When the transaction is closed, all references to
those pages are redirected outside of the transaction.

class Borges::Transaction < Borges::Filter
  def initialize
    @active =3D true
  end

  def close
    @active =3D false
  end

  def handle_request_in(req, session)
    if @active then
      req
    else
      session.page_expired
    end
  end
end

You may have noticed that there is no storage of pages inside the
transaction itself.  Borges knows which filters where used with a
particular request, and restores them appropriately.

There also is a 'Once' filter, which only allows a page to be shown a
single time:

class Borges::Once < Borges::Filter
  def initialize
    @seen_keys =3D []
  end

  def handle_request_in(req, session)
    if @seen_keys.include? req.action_key then
      session.page_expired
    else
      @seen_keys << req.action_key
    end
  end
end

Both types of filters have handy helper methods on Session to let you
instantiate them easily.

--=20
Eric Hodel - drbrain@segment7.net - http://segment7.net
All messages signed with fingerprint:
FEC2 57F1 D465 EB15 5D6E  7C11 332A 551C 796C 9F04


--tuYRN1zEaS85jg/Y
Content-Type: application/pgp-signature
Content-Disposition: inline

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.2 (FreeBSD)

iD8DBQFAnJUfMypVHHlsnwQRAlCJAKDxqK651UuABTIWOdZQr4/m+ne0GACfdMI7
ViqjxqZOs8v8GDbfM/9GaOE=
=SuBs
-----END PGP SIGNATURE-----

--tuYRN1zEaS85jg/Y--