[ZPatterns] Revisiting an old question: Reusable ZPatterns applications

[Steve Alexander]

I'd just composed a reply to this, when we had a 2 hour power-cut :-/

Here goes my second try.

Itai Tavor wrote:
 >

> Second, and this is where the whole thing becomes quite impossible, 
> there's the problem of upgrading the application, for bug fixes or 
> feature changes. With a normal app, you install a new copy, refresh the 
> product, and you got the new application working with all your existing 
> data. 


My procedure for this goes like this:

1: Export data from Racks to an xml file on the filesystem
2: Install new Data.fs / Zope+Python+Data.fs+External Methods etc.
3: Reimport data from Racks
4: Update Catalogs (in dependency order) from the ids in the imported data

Note that when I say "export as xml", I mean to a domain-specific xml 
DTD using an external method.

The advantage of this is that it is easy to migrate the application 
between very different schemas. I needed to do this when I converted an 
application from Specialists+Racks and Customizers to just 
Specialists+Racks.

--
Steve Alexander
Software Engineer
Cat-Box limited