Genesis architectureΒΆ

Tags: plone

Genesis is the next version of archgenxml . I used to call it agx 2.0, but I've since been cured of my evils :-)

Daniel Nouri stirred up the conversation on the archetypes development mailinglist this afternoon, prompting me to finally write down the architecture a bit. Good thing he did it.

Design

Genesis has two basic steps: reading and writing. Reading the input UML file and putting it into an internal model. And secondly writing out the actual product from that internal model to the filesystem. Simple, huh?

There are some configuration possibilities to steer this process. Of course some commandline or config file parameters for setting some global options. More directly important are the profiles and the generator.

Profiles
A profile is used to define what you're saying in your UML model. Basic classes and attributes are OK, but you want to be able to say "hey, this is no ordinary class, this is really a CMFMember class" - with all the associated differences in handling.

You can define your UML stereotypes and tagged values in a profile. Such a profile of course forces you to document those items, so that we won't ever have the bad undocumented days back! It is possible to mix profiles, so you can have a plone 2.1 profile plus a Membrane profile.

The stereotypes defined in your profile(s) change the classes in the internal model. Instead of only providing an IGenericClass interface, they now also provide, say, a ICMFMemberClass interface. This will be used by the subsequent generator step.

Did I mention that you can make your own profiles? You've got to add support for it in the generator, too. This gives you previously unknown customisation possibilities :-)

Generator
This isn't too well-defined yet. There are two ways to tackle this: making an in-memory representation of what's to be written out or doing it in an almost xslt-like push/pull way. I'm way in favour of ding it the push/pull way, so I'll blatantly describe that here.

For a certain profile, say plone 2.1, there are a number of fixed files and directories that need to be generated. The generator tries to create them and actively pulls information from the internal model. An adapter for the main model element might be best here. This gives you the Extensions/install.py for instance.

The second step is for the internal model to push all items to the generator and have the generator slug it out. There has to be a configuration file that tells the generator that for every incoming IPloneClass, there should be an archetypes class, possibly a template in the skins directory and so on.

All those little things like an __init__.py file in every directory are handled by creating it on every incoming IPackage. The adapter itself can of course query the package for contained items and calling an appropriate adapter that gives back an import line.

The great thing here is that if you've got a certain class of item in the package for which you don't want an import line then you just need to provide an adapter for that interface that keeps quiet when asked for an import line.

So: genesis reads a file into an internal model, using one or more profiles. Those profiles customise the base genesis to your needs. It then uses a generator (which you again configure) to create your product.

Profiles, the generator configuration and adapters look set to making this pretty adaptable, maintainable and elegant.

Current state of the code

The current code is nowhere near finished. About half of it is in the state that we left it when running for the train after September's castle sprint. I've done some work on a few parts. The parts that start to look a bit decent:

Internal model
It can store most basic UML-like items. Stereotypes get turned into implemented interfaces, ready for the generator to use.
Profiles
Used to define profiles of stereotypes and tagged values. Also includes documentation for those items.
Option/configparser
Mostly copy-pasted from the existing code.

I've only recently started trying to wire it all together a bit, so stay tuned for more improvements. Jean-Paul Ladage plans on sitting with me for half a day a week to push it forward to get some basic functionality going before the golden roof sprint .

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My name is Reinout van Rees and I work a lot with Python (programming language) and Django (website framework). I live in The Netherlands and I'm happily married to Annie van Rees-Kooiman.

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