Zope + Ape + Subversion (was: RE: [Zope-dev] Using a truely
revis ion based storage for Zope ?)
Kapil Thangavelu
hazmat at objectrealms.net
Wed Apr 14 07:02:20 EDT 2004
granted the svn integration has lots of coolness factors including
richer client integration, but things like zope version control
(zope.org cvs) are already production quality and not so hard to
integrate in for basic version control.
-kapil
On Tue, 2004-04-13 at 14:13, Arthur Chan Chi Chuen wrote:
> Hi all,
>
> I've read your discussion about version control, it seems a cool thing you
> guys making good progress. Btw, can I ask is the Ape using Subversion in Zope
> stable? how able CMF stuff? I wanna make/find a document management system
> which can provide some kinda version control in Plone.
>
> Thanks
> Arthur
> On Tue, 13 Apr 2004 04:06:26 -0400, Kapil Thangavelu wrote
> > On Mon, 2004-04-12 at 18:03, Jean-Francois.Doyon at CCRS.NRCan.gc.ca wrote:
> > > G'Day,
> > >
> > > Well, step one is done ... I now have Zope + Ape using Subversion as it's
> > > "filesystem" !!
> > >
> >
> > cool!
> >
> > > This is step one because, as Shawn suggested (Thanks for the pointer,
> that's
> > > what I needed!), this simply means that Zope uses SVN purely as a
> > > filesystem.
> > >
> >
> > > Because of subversion's nature, I want to look at 2 things beyond this
> that
> > > traditional filesystems don't support:
> > >
> > > - Use zope's username for SVN logging.
> >
> > using AccessControl.getSecurityManager().getUser().getId() and
> > setting it up as a revision prop ( or directly when creating the
> > repo transaction) should do it.
> >
> > > - History/Undo support: View past revisions of an object, and revert to
> such
> > > a past revision.
> >
> > perhaps the code for this would be helpful, (remove image for code
> > link)
> http://zope.org/Members/k_vertigo/Products/CMFSubversionBrowser/FileRevisions.
> png
> >
> > > - Zope Version support: SVN is fully transactional and atomic, this should
> > > allow for support of Zope versions (I think ?)
> > >
> >
> > zope version support isn't really all that worthwhile, esp in a cmf
> > context. in general zope's version support (or zodb more
> > particularly) is a database level feature masquerading as an
> > application one. since objects modified in a version are in essence
> > locked from participating in other transactions, actions like
> > modifying content in a version in a cmf site amounts to locking the
> > catalog from changes outside of the version, which amounts to
> > shutting down write activities to a cmf site. otoh, integration with
> > zope's transaction manager would be a good thing, although its
> > problematic to integrate between svn and zope txn models, more on
> > that in a moment.
> >
> > > In the longer term, there's great opportunity for:
> > >
> > > - "Built-in" conflict management and resolution: No more need for a
> > > "SafetyBelt" type approach. Right now I haven't looked at this at all. I
> > > plan to implement smart merging where possible (It might work already
> > > actually, I just need to test it). True conflicts (Where a merge can't be
> > > accomplished withouth user interaction) would raise some sort of conflict
> > > error.
> > >
> >
> > i don't know that conflict management is really useful in this context.
> > svn like zope relies on optimistic concurrency control, and currently
> > doesn't support dav locking (which zope does). ie, it will just
> > throw an error if the content has been changed since the transaction
> > began. the 'normal' concurrency control of svn is better but
> > dependent on using the working copy (wc) layer, which is additional
> > programming and storage overhead. so at the layer of the svn client
> > this is already done and working and good, but integrating this
> > functionality into zope is a bit harder without wc overhard.
> >
> > this also makes the transaction integration becomes harder because both
> > zope and svn are using what amounts to optimistic concurrency control
> > which makes it impossible afaics, to get real txn integration, ie in
> > zope's two phase commit strategy, the last chance for a participant
> > to safely abort is tpc_vote, but there is no real way of knowing if
> > the svn txn will suceed or not until its tried. if it is tried at
> > this stage and succeeds then there is the possibility of a latter
> > txn participant failing the tpc_vote and the txn being aborted, and
> > if waits till tpc_finish (last part of two phase commit) and the svn
> > txn fails it can hose the composite txn integrity.
> >
> > once svn supports dav locks, doing txn integration via resource locking
> > as part of tpc_vote (or earlier) would be possible, till then.. i
> > dunno, i can't see a way around this for real txn integration.
> >
> > i'm also curious how you dealt with svn transactions as part of the ape
> > integration work to date.
> >
> > > - Editing Zope content objects through interaction with the svn
> repository.
> > > I can checkout the repository, edit some objects, and chek them back in,
> > > never interacting with Zope directly ... I've already tried this ! Works
> > > great for text based content types such as PageTemplates or DTML Documents
> > > and so on ... I even did it with a JPG, though because the properties hold
> > > width and height, you get some weird looking pictures :) The concept is
> > > valid though. There may someday be a way to leverage this functionality
> > > better with a purpose built client of some sort.
> >
> > to me this is one of the fundamental benefits of using svn, giving users
> > the ability to use interfaces like tortoisesvn (win shell extensions)
> > or mac finder extensions to interact directly with content.
> >
> > >
> > > - Leveraging SVN's property management. Content in SVN has properties,
> much
> > > like Zope does. I haven't looked at it yet, but I've
> noticed ".properties"
> > > file appearing ... I'm guessing those are the Zope properties, which would
> > > be better handled by subversion's property mechanism. And properties are
> > > versioned too !
> >
> > definitely!
> >
> > >
> > > In the realm of the wishful thinking, there's even more:
> > >
> > > Right now, HEAD (Latest/youngest revision) is always used and worked with.
> > > The really powerful feature I want to eventually get to is publsihing
> > > something of a given revision, while editing another. One potential
> > > paradigm for distiguishing between the two modes of operation could be to
> > > use anonymous vs. authenticated. This is not useful to everyone, but can
> be
> > > in certain circumstances, most notably where authenticated =
> > > authors/developpers and anonymous = normal users. This however requires
> ZMI
> > > interfaces, and in my case CMF ones as well ... This would be global
> though
> > > ... Eventually it'd be nice to have per object control of this stuff.
> Andy
> > > McKay says it can't be done, anybody care to contradict him ? :P I image
> I'd
> > > have to monkey pathc something DEEP in the Zope code base, but I find the
> > > mix-in class that's the commonn denominator ... why not ?
> > >
> >
> > to me this seems a separate point then svn usage at all, its really
> > about content view paradigms for revision workflow. the two predominant
> > ones are using staging to deploy different sites representing different
> > parts of the publication cycle/wf, and the other which afaik, is only
> > widely used by silva is view multiplexing where the view of a
> > content is responsible for retrieving the proper version to render a
> > display for, although afaicr silva support for such is initimately
> > tied to its workflow and versioning paradigm.
> >
> > > Anyways, I'm just rambling by now ... Comments, thoughts and constructive
> > > criticism welcome !
> >
> > i've done some thinking and work with integration of svn as content
> > in zope as well, though using a different software stack than ape. some
> > notes/ideas culled from a dev diary i kept while working on it that
> > might be useful.
> >
> > - using svn hook scripts for event notification back into zope (content
> > reindex), although it should be careful about modifying the content
> > otherwise some client which just committed might be put out of date.
> >
> > - transform layers (using portal transforms) with a private content type
> > registry... although integrating at the ape layer this might not be
> > as useful.
> >
> > cheers,
> >
> > -kapil
> >
> > >
> > > Thanks,
> > > J.F.
> > >
> > > -----Original Message-----
> > > From: zope-dev-bounces at zope.org [mailto:zope-dev-bounces at zope.org]On
> > > Behalf Of Shane Hathaway
> > > Sent: April 8, 2004 11:20 AM
> > > To: Jean-Francois.Doyon at ccrs.nrcan.gc.ca
> > > Cc: zope-dev at zope.org
> > > Subject: Re: [Zope-dev] Using a truely revision based storage for Zope ?
> > >
> > >
> > > Jean-Francois.Doyon at CCRS.NRCan.gc.ca wrote:
> > > > I've started looking at the ZODB and APE packages to try and get some
> > > > understanding of how the whole storage interaction works, but it'll take
> > > me
> > > > some time to figure it all out ... So I thought I'd get feedback on the
> > > idea
> > > > first ...
> > >
> > > Sounds great! If I were you, I would start by replacing
> > > Ape/lib/apelib/fs/fileops.py with something that uses the Subversion
> > > module. It's a very simple module and you should be able to get pretty
> > > far that way.
> > >
> > > Shane
> >
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