David Glick: Building Content Types with Dexterity

Over the past year and a half, Martin Aspeli and company have been hard at work creating Dexterity, the next-generation framework for developing content types in Plone. In this tutorial, you learn the basics of building content types with Dexterity, how it compares to Archetypes, and the current status of the project.

I am working for groundwire, formerly known as ONe/Northwest.

A content type is for example a page, document or image. It has a schema, custom view templates, miscelaneous settings (can you search for it, can you add comments, etc).

History lesson. CMF (Content Management Framework) is an underlying framework for registering types, assigning workflows. Not schema based. Archetypes came along and provided schemas, with schema based form generation. Not going away anytime soon. But it has some ugly bits. Not easy as basis for generating schemas TTW (through the web).

At the Plone Planning Summit we talked about how we were going to create content types in the future, still archetypes or not. So after that, Martin Aspeli started the Dexterity project. Make it possible to define a content type through the web, export it to the file system and be able to do this the other way around as well.

Products.Archetypes is big. plone.dexterity is small and you can extend it with just the extra parts you need.

Archetypes does a lot of what seems to be magic; a lot of code, like factories and methods, that are created on the fly.

Installing dexterity: add the plone.app.dexterity egg in your buildout.cfg and add http://good-py.appspot.com/release/dexterity/1.0a2 in your buildout extends lines.

Options for extending a content type are subclassing, archetypes.schemaextender, and now with dexterity you have a new concept called behaviors. A behavior can be something like: create the short name of the object from the title; add geolocation; add ownership.

You have to watch out when changing a content type, as existing objects are not automatically updated, for instance when you change a field name.

We don't create custom Add permissions yet through the web.

Example package: example.ploneconf09 at http://svn.plone.org/svn/plone//plone.dexterity/example.ploneconf09

The type definition can just be exported via portal_setup by exporting the types tool. We want some new UI for this. The schema will be in there, in escaped xml. You can also put this in a separate xml file, or define a zope 3 schema--use plone.directives.form for this.

Using a zope 3 schema: add five.grok as dependency and add package="." /> to your zcml. To move a field to a different fieldset, specify form.fieldset in the schema and list the fields you want to have on this tab.

With plone.directives.dexterity you can define read and write permissions.