Fred van Dijk: 7 things that can surprise you when you start customising or developing for Plone

This is a basic rundown and summary of our beloved subjects like ZODB persistence. Traversal. The view/viewlet/portlet trinity. How is a call handled in Plone. The differences between zcml and generic setup. Utilities and the ZCA. restrictedTraverse. The Plone catalog.

These are surprises that I have encountered myself, or that I have seen on faces of people I have trained or worked with during the years.

1. Everything can or could be done through the web (TTW).

Zope vision from the nineties. Why don't we use this dynamic language called Python so we can change things TTW? It's so easy.

2. The learning curve.

It starts easy, but then you hit what we call a Z-shaped learning curve. Dynamic Python makes things easy, and then it makes things hard, at least when you put Zope on it, then CMF, then Plone. Plone the product on top of a CMS on top of a framework on top of a language. We have a product, a framework, a stack, so it is hard.

3. Five levels of conceptual complexity.

It helps to teach all the levels. Give new users a drawer for each level, so they have a box that they can put some info in.

You have:

• browser: html, css, js
• frontend: transforms, templates, zpt, metal, diazo
• application logic: views, viewlets, portlets, adapters, Zope Component Architecture
• dynamism: GenericSetup, zcml, xml, zope schema
• programming language: Python, buildout, pip
• package WorkManager (OS): apt, rpm

4 Same language/formats on different levels:

• XML is used for the ZCA, GS, zope.schema, Diazo rules
• package manager: buildout, pip, setuptools, GS

But: there is no magic. It is just advanced technology.

Startup:

• Python uses sys.path modules to start bin/instance
• ZCA loads site.zcml, package includes, other zcml to change configuration.
• Then we have a runtime environment with objects and classes, the ZODB. GenericSetup is then some XML that you can use to change the ZODB.

So the ZCA overrides components in runtime. The alternative is to edit core files, maybe compile them, and restart. Much less nice and not sustainable.

So now we have a Plone process running.

5. Zope is not that complicated.

Over HTTP Zope gets a request, does traversal, finds an object in the ZODB, loads it in memory. Then on top of this object we show a browser view / template. The template hooks into a main template, maybe does some sub requests, some Diazo, and we end up with some html and we are done.

This is all still 'lies to children'. It is simplified until we are able to understand more. With increment exposure to these concepts, it will stick more. It is complicated, but there is no magic.

6. Acquisition.

It is traversal in the wrong direction.

7. When you try to explain things, you improve your own understanding.

There is so much Plone content online: training, docs, youtube, github, discourse. We all learn in different ways, with own preferences, reading, viewing. There are so many repositories on github that you can explore for new ideas. Just yesterday Philip did a talk about exportimport and afterwards I did it, but from a different angle. It helps.

The community is our biggest asset.