[Zope] Re: Zope 2 and Zope 3

Thu Feb 15 05:50:38 EST 2007

Geoff Gerrietts wrote:
[some paragraphs about scaling which I can't really comment on]

>> As for source control, I figure all of your code (DTML, yuck) is in the
>> ZODB. This went out of fashion a long time ago, most serious development
>> happens on the filesystem (in Python packages) which can obviously be
>> source-controlled very well.
> 
> A good deal of the code is in the ZODB, because it's (yuck) DTML
> documents, yes. We have another sizable chunk that lives on the
> filesystem. The challenge in managing the build/deploy process has
> been trying to find a way to keep those two conjoined. I suspect that
> any dependency on the ZODB at all is likely to be considered an
> impediment, and my quick eyeballing says it's not gone or even really
> optional under Zope 3 (but I'm sure we could work something out.)

The ZODB is still there in Zope 3, but Zope 3 is much less dependent on 
it. In fact, there are people who are using Zope 3 without any ZODB 
instance at all, but directly talk to a relational database. Currently 
this requires a bit of hacking, but our good man Chris Withers has 
expressed interest in making the next release of Zope 3 more flexible in 
this regard.

What's already possible is to have a minimal ZODB with only one 
persistent object: a SQLObject or SQLAlchemy container. That's a 
container (e.g. like a folder) whose items aren't persisted in the ZODB 
but come from a relational database.

You seem to already have come to the conclusion that having code live in 
both the filesystem and the ZODB can be painful. I think a good first 
step for you would be to migrate your remaining ZODB-based code to the 
filesystem. That not only makes deployment easier, you're also free to 
refactor it then (e.g. using Zope 3 idioms). In the long run, this also 
means saying good-bye to things like External Methods because they 
require code on the filesystem and configuration in the ZODB.

>> Regarding "oh you'll hafta start over", it's pretty much true, if you
>> want to switch to Zope 3. But nobody says you have to. You can do it
>> incrementally by porting some of your app's functionality to Zope 3
>> components step by step (as mentioned already, most work in Zope 2). Big
>> projects like Plone aren't rewriting their whole codebase either, but
>> new development is completely Zope3-based. Their target platform still
>> is Zope 2, though.
> 
> "You'll hafta start over" is only ever true in degrees, though, and
> I'm still trying to figure out what the degrees are. The business
> logic will still be the same. Can we hack together a DTML processor
> that allows us to export the DTML documents to the filesystem and
> publish them from there? Maybe, I don't know. Did someone else already
> do that? Don't know that either. How dramatically will our products
> need to change? Probably 75% of our Python code is written in a
> bastardized form of ExternalMethod; we might be able to leverage that
> unfortunate architectural choice to significant advantage during our
> porting phase. These are the kinds of questions I have, and I think
> the answers probably aren't easy or someone would have offered them
> up.

It is certainly possible to execute filesystem-based DTML (using 
Globals.DTMLFile). It's hard to say how much your products will have to 
change without knowing the codebase. If you have external methods, it 
shouldn't be too hard to refactor this code into components in "proper" 
Python modules. To make things easy, the external methods could stay at 
first, for backwards compatibility. I would take this one step at a time 
(that's at least what everybody else seems to do and it looks like it's 
working out for everybody).

> Someone's going to need to learn enough Zope 3 to answer the
> questions. I'm not sure it will be me, but maybe. :)

Well, whoever it'll be, there are books (e.g. http://worldcookery.com) 
and trainings (e.g. http://trizpug.org/boot-camp/camp5) that should help 
with the learning :).

-- 
http://worldcookery.com -- Professional Zope documentation and training
Next Zope 3 training at Camp5: http://trizpug.org/boot-camp/camp5