Schema-driven types

Creating a minimal type based on a schema

The schema

A simple Dexterity type consists of a schema and an FTI (Factory Type Information, the object configured in portal_types in the ZMI). We’ll create the schemata here, and the FTI on the next page.

Each schema is typically in a separate module. Thus, we will add three files to our product: presenter.py, program.py, and session.py. Each will start off with a schema interface.

Creating base files

Since we created our example.conference command via ZopeSkel, we'll be able to use its addcontent command to add base files for our content types. addcontent must be used from inside your new package.

Note

If you didn't use ZopeSkel, you'll need to add the files yourself. We'll supply the full source here, and you may refer to the example repository.

Typical addcontent use starting out at the buildout directory is:

$ cd src/example.conference/
$ ../../bin/paster addcontent -l
Available templates:
    dexterity_behavior:  A behavior skeleton
    dexterity_content:   A content type skeleton

The "-l" lists available content templates.

Note

At this point, you may receive an error message beginning with pkg_resources.DistributionNotFound. Do not follow the error messages advice to run python setup.py. Instead, check to make sure that you have added your package to the eggs and develop sections of your buildout and have run buildout. This loads package dependencies that are required to run addcontent.

Now, let's add two of the three content types, for the conference sessions and programs. We'll do presenters in the next section as a model-driven type.

$ ../../bin/paster addcontent dexterity_content
Enter contenttype_name (Content type name ) ['Example Type']: Session
Enter contenttype_description (Content type description ) ['Description of the Example Type']: A session in a conference
Enter folderish (True/False: Content type should act as a container ) [False]: False
Enter global_allow (True/False: Globally addable ) [True]: False
Enter allow_discussion (True/False: Allow discussion ) [False]:

$ ../../bin/paster addcontent dexterity_content
Enter contenttype_name (Content type name ) ['Example Type']: Program
Enter contenttype_description (Content type description ) ['Description of the Example Type']: A conference program
Enter folderish (True/False: Content type should act as a container ) [False]: True
Enter global_allow (True/False: Globally addable ) [True]:
Enter allow_discussion (True/False: Allow discussion ) [False]:

Notice that we chose to make the Conference type a container, because we will want it to be able to contain sessions. Likewise, we set Globally addable` for the Session type to False, as we'll only want to allow them to be added inside programs.

If you check example.conference/example/conference, you'll discover that Python source files program.py, session.py and presenter.py have been added. If you explore example.conference/example/conference/profiles/default/types, you'll also find XML files setting the Factory Type Information for each new type. We'll customize all of these.

Setting the schema

Start with program.py. Notice the boilerplate:

# If you want a schema-defined interface, delete the model.load
# line below and delete the matching file in the models sub-directory.
# If you want a model-based interface, edit
# models/program.xml to define the content type
# and add directives here as necessary.

model.load("models/program.xml")

Since we're going to be defining our fields via Zope schema rather than an XML model, delete all of that.

Next, add schema declarations for our fields. The top part of the file should look like:

from example.conference import MessageFactory as _
from five import grok
from plone.app.textfield import RichText
from plone.supermodel import model
from zope import schema


class IProgram(model.Schema):
    """A conference program. Programs can contain Sessions.
    """

    title = schema.TextLine(
            title=_(u"Program name"),
        )

    description = schema.Text(
            title=_(u"Program summary"),
        )

    start = schema.Datetime(
            title=_(u"Start date"),
            required=False,
        )

    end = schema.Datetime(
            title=_(u"End date"),
            required=False,
        )

    details = RichText(
            title=_(u"Details"),
            description=_(u"Details about the program"),
            required=False,
        )

We've also removed unnecessary import declarations.

If you haven't developed for Plone before, take special note of the from example.conference import MessageFactory as _ code. This is to aid future internationalisation of the package. Every string that is presented to the user should be wrapped in _() as shown with the titles and descriptions below.

The message factory lives in the package root __init__.py file:

from zope.i18nmessageid import MessageFactory

_ = MessageFactory("example.conference")

Notice how we use the package name as the translation domain.

Notice how we use the field names title and description for the name and summary. We do this to provide values for the default title and description metadata used in Plone’s folder listings and searches, which defaults to these fields. In general, every type should have a title field, although it could be provided by behaviors (more on those later).

Save program.py.

session.py for the Session type should look like this:

from example.conference import MessageFactory as _
from five import grok
from plone.app.textfield import RichText
from plone.supermodel import model
from zope import schema


class ISession(model.Schema):
        """A conference session. Sessions are managed inside Programs.
        """

        title = schema.TextLine(
                title=_(u"Title"),
                description=_(u"Session title"),
            )

        description = schema.Text(
                title=_(u"Session summary"),
            )

        details = RichText(
                title=_(u"Session details"),
                required=False
            )

Note that we haven’t added information about speakers or tracks yet. We’ll do that when we cover vocabularies and references later.

Schema interfaces vs. other interfaces

As you may have noticed, each schema is basically just an interface (zope.interface.Interface) with fields. The standard fields are found in the zope.schema package. You should look at its interfaces (parts/omelette/zope/schema/interfaces.py) to learn about the various schema fields available, and review the online documentation for the package. You may also want to look up plone.namedfile, which you can use if you require a file field, plone.app.relationfield, which can be used for references, and plone.app.textfield, which supports rich text with a WYSIWYG editor. We will cover these field types later in this manual. They can also be found in the reference at the end.

Unlike a standard interface, however, we are deriving from model.Schema (actually, plone.supermodel.model.Schema). This is just a marker interface that allows us to add some form hints to the interface, which are then used by Dexterity (actually, the plone.autoform package) to construct forms. Take a look at the plone.autoform documentation to learn more about the various hints that are possible. The most common ones are form.fieldset(), to define groups of fields, form.widget(), to set a widget for a particular field, and form.omit() to hide one or more fields from the form. We will see examples of these later in the manual.

The FTI

Adding a Factory Type Information object for the type

With the schema in place, we just need to make our types installable. We do this with GenericSetup. Most of this was set up when we used addcontent to add the content type boilerplate.

Look in the types.xml file in your packages example/conference/profiles/default directory:

<object name="portal_types">
 <object name="example.conference.program" meta_type="Dexterity FTI" />
 <object name="example.conference.session" meta_type="Dexterity FTI" />
</object>

We use the package name as a prefix and the type name in lowercase to create a unique name. It is important that the meta_type is Dexterity FTI.

We then need to add/edit an XML file for each of the types, where the file name matches the type name.

The Session type, in example.conference.session.xml, should look like this:

<?xml version="1.0"?>
<object name="example.conference.session"
   meta_type="Dexterity FTI"
   i18n:domain="example.conference" xmlns:i18n="http://xml.zope.org/namespaces/i18n">

  <!-- Basic metadata -->
  <property name="title" i18n:translate="">Session</property>
  <property name="description"
    i18n:translate="">A session in a program</property>
  <property name="icon_expr">string:${portal_url}/document_icon.png</property>
  <property name="factory">example.conference.session</property>
  <property name="global_allow">False</property>
  <property name="filter_content_types">True</property>
  <property name="allowed_content_types" />
  <property name="allow_discussion">False</property>

  <!-- schema and class used for content items -->
  <property name="schema">example.conference.session.ISession</property>
  <property name="klass">example.conference.session.Session</property>

  <property name="behaviors">
     <element value="plone.app.content.interfaces.INameFromTitle" />
   </property>

  <!-- View information -->
  <property name="link_target"></property>
  <property name="immediate_view">view</property>
  <property name="default_view">view</property>
  <property name="view_methods">
   <element value="view"/>
  </property>
  <property name="default_view_fallback">False</property>
  <property name="add_permission">cmf.AddPortalContent</property>


  <!-- Method aliases -->
  <alias from="(Default)" to="(dynamic view)" />
  <alias from="view" to="(selected layout)" />
  <alias from="edit" to="@@edit" />
  <alias from="sharing" to="@@sharing" />

  <!-- Actions -->
  <action title="View" action_id="view" category="object" condition_expr=""
    url_expr="string:${object_url}/" visible="True">
    <permission value="View" />
  </action>
  <action title="Edit" action_id="edit" category="object" condition_expr=""
    url_expr="string:${object_url}/edit" visible="True">
    <permission value="Modify portal content" />
  </action>
</object>

There is a fair amount of boilerplate here which could actually be omitted, because the Dexterity FTI defaults will take care of most of this. However, it is useful to see the options available so that you know what you can change.

The important lines here are:

• The name attribute on the root element must match the name in types.xml and the filename.
• We use the package name as the translation domain again, via i18n:domain.
• We set a title and description for the type
• We also specify an icon. Here, we use a standard icon from Plone’s plone_images skin layer. You’ll learn more about static resources later.
• We have set global_allow to False, since these objects should only be addable inside a Program..
• The schema interface is referenced by the schema property.
• We set the klass property to the class defined in the boilerplate file. If you were creating this yourself, you could have instead just used plone.dexterity.content.Item or plone.dexterity.content.Container.
• We specify the name of an add permission. The default cmf.AddPortalContent should be used unless you configure a custom permission. Custom permissions are convered later in this manual.
• We add a behavior. Behaviors are re-usable aspects providing semantics and/or schema fields. Here, we add the INameFromTitle behavior, which will give our content object a readable id based on the title property. We’ll cover other behaviors later. We removed the IBasic behavior (which would supply title and description fields) as we have alternative fields.

The Program, in example.conference.program.xml, looks like this:

<?xml version="1.0"?>
<object name="example.conference.program"
   meta_type="Dexterity FTI"
   i18n:domain="example.conference" xmlns:i18n="http://xml.zope.org/namespaces/i18n">

  <!-- Basic metadata -->
  <property name="title" i18n:translate="">Program</property>
  <property name="description"
    i18n:translate="">Conference Program</property>
  <property name="icon_expr">string:${portal_url}/folder_icon.png</property>
  <property name="factory">example.conference.program</property>
  <property name="global_allow">True</property>
  <property name="filter_content_types">True</property>
  <property name="allowed_content_types">
      <element value="example.conference.session" />
  </property>
  <property name="allow_discussion">False</property>

  <!-- schema and class used for content items -->
  <property name="schema">example.conference.program.IProgram</property>
  <property name="klass">example.conference.program.Program</property>

  <property name="behaviors">
     <element value="plone.app.content.interfaces.INameFromTitle" />
   </property>

  <!-- View information -->
  <property name="link_target"></property>
  <property name="immediate_view">view</property>
  <property name="default_view">view</property>
  <property name="view_methods">
   <element value="view"/>
  </property>
  <property name="default_view_fallback">False</property>
  <property name="add_permission">cmf.AddPortalContent</property>


  <!-- Method aliases -->
  <alias from="(Default)" to="(dynamic view)" />
  <alias from="view" to="(selected layout)" />
  <alias from="edit" to="@@edit" />
  <alias from="sharing" to="@@sharing" />

  <!-- Actions -->
  <action title="View" action_id="view" category="object" condition_expr=""
    url_expr="string:${object_url}/" visible="True">
    <permission value="View" />
  </action>
  <action title="Edit" action_id="edit" category="object" condition_expr=""
    url_expr="string:${object_url}/edit" visible="True">
    <permission value="Modify portal content" />
  </action>
</object>

We've edited this one a little from the boilplate: the difference here is that we filter the containable types (filter_content_types and allowed_content_types) to allow only Sessions to be added inside this folder.

Testing the type

How to start up Plone and test the type, and some trouble-shooting tips.

With a schema and FTI for each type, and our GenericSetup profile registered in configure.zcml, we should be able to test our type. Make sure that you have run a buildout, and then start ./bin/instance fg as normal. Add a Plone site, and go to the portal_quickinstaller in the ZMI. You should see your package there and be able to install it.

Once installed, you should be able to add objects of the new content types.

If Zope doesn’t start up:

• Look for error messages on the console, and make sure you start in the foreground with ./bin/instance fg. You could have a syntax error or a ZCML error.

If you have a failed import for plone.directives.form, make sure that you specified the [grok] extra for plone.app.dexterity in your setup.py install_requires.

If you don’t see your package in portal_quickinstaller:

• Ensure that the package is either checked out by mr.developer or that you have a develop line in buildout.cfg to load it as a develop egg. develop = src/* should suffice, but you can also add the package explicitly, e.g. with develop = src/example.conference.
• Ensure that the package is actually loaded as an egg. It should be referenced in the eggs section under [instance] .
• You can check that the package is correctly configured in the buildout by looking at the generated bin/instance script (bin\instance-script.py on Windows). There should be a line for your package in the list of eggs at the top of the file.
• Make sure that the package’s ZCML is loaded. You can do this by installing a ZCML slug (via the zcml option in the [instance] section of buildout.cfg) or by adding an <include /> line in another package’s configure.zcml. However, the easiest way with Plone 3.3 and later is to add the z3c.autoinclude.plugin entry point to setup.py.
• Ensure that you have added a <genericsetup:registerProfile /> stanza to configure.zcml.

If the package fails to install in portal_quickinstaller:

• Look for errors in the error_log at the root of the Plone site, in your console, or in your log files.
• Check the syntax and placement of the profile files. Remember that you need a types.xml listing your types, and corresponding files in types/*.xml.

If your forms do not look right (e.g. you are missing custom widgets):

• Make sure your schema derives from model.Schema.
• Remember that the directives require you to specify the correct field name, even if they are placed before or after the relevant field.
• Check that you have a <grok:grok package="." /> line in configure.zcml.