Sometimes, it is useful for objects that provide a particular behavior
to also provide a specific marker interface. For example, you can
register a viewlet for a particular marker and use a behavior to enable
that marker on all instances of a particular content type. The viewlet
will then only show up when the behavior is enabled. The same principle
can be applied to event handlers, views and other components.
Note
There is usually no need to use markers to enable a custom adapter since
a standard behavior is already a conditional adapter. However, in
certain cases, you may want to provide one or more adapters to an
interface that is not the behavior interface, e.g. to use a particular
extension point provided by another component. In this case, it may
easier to set a marker interface and provide an adapter from this
marker.
Primary marker behaviors
In the first case, where the behavior interface and the marker interface
are the same, you can simply use the <plone:behavior />*directive
without a *factory. For example:
<plone:behavior
title="Pony viewlet"
description="Shows a pony next to the content"
provides=".behaviors.IWantAPony"
/>
One could imagine a viewlet based on plone.pony registered for the
IWantAPony marker interface. If the behavior is enabled for a
particular object, IWantAPony.providedBy(object) would be true.
Supplementary marker behaviors
In the second case, we want to provide a behavior interface with a
behavior adapter factory as usual (e.g. with some form fields and a
custom storage or a few methods implemented in an adapter), but we also
need a custom marker. Here, we use both the provides and marker
attributes to <plone:behavior /> to reference the two interfaces, as
well as a factory.
To show a slightly more interesting example, here is a behavior from a
project that lets content authors with particular permissions
(iz.EditOfficialReviewers and iz.EditUnofficialReviewers), nominate
the “official” and any “unofficial” reviewers for a given content item.
The behavior provides the necessary form fields to support this, but it
also sets a marker interface that enables an ILocalRoleProvider
adapter to automatically grant local roles to the chosen reviewers, as
well as a custom indexer that lists the reviewers.
The ZCML registration looks like this:
<plone:behavior
title="Reviewers"
description="The ability to assign a list of official and/or unofficial reviewers to an item, granting those users special powers."
provides=".reviewers.IReviewers"
factory="plone.behavior.AnnotationStorage"
marker=".reviewers.IReviewersMarker"
/>
Notice the use of the AnnotationStorage factory. This is a re-usable
factory that can be used to easily create behaviors from schema
interfaces that store their values in annotations. We’ll describe this
in more detail later. We could just as easily have provided our own
factory in this example.
This whole package is grokked, so in configure.zcml we have:
<grok:grok package="." />
The reviewers.py module contains the following:
"""Behavior to enable certain users to nominate reviewers
Includes form fields, an indexer to make it easy to find the items with
specific reviewers, and a local role provider to grant the Reviewer and
OfficialReviewer roles appropriately.
"""
from five import grok
from zope.interface import alsoProvides, Interface
from plone.directives import form
from zope import schema
from plone.formwidget.autocomplete.widget import AutocompleteMultiFieldWidget
from borg.localrole.interfaces import ILocalRoleProvider
from plone.indexer.interfaces import IIndexer
from Products.ZCatalog.interfaces import IZCatalog
from iz.behaviors import MessageFactory as _
class IReviewers(form.Schema):
"""Support for specifying official and unofficial reviewers
"""
form.fieldset(
'ownership',
label=_(u'Ownership'),
fields=('official_reviewers', 'unofficial_reviewers'),
)
form.widget(official_reviewers=AutocompleteMultiFieldWidget)
form.write_permission(official_reviewers='iz.EditOfficialReviewers')
official_reviewers = schema.Tuple(
title=_(u'Official reviewers'),
description=_(u'People or groups who may review this item in an official capacity.'),
value_type=schema.Choice(title=_(u"Principal"), source="plone.principalsource.Principals"),
required=False,
missing_value=(), # important!
)
form.widget(unofficial_reviewers=AutocompleteMultiFieldWidget)
form.write_permission(unofficial_reviewers='iz.EditUnofficialReviewers')
unofficial_reviewers = schema.Tuple(
title=_(u'Unofficial reviewers'),
description=_(u'People or groups who may review this item in a supplementary capacity'),
value_type=schema.Choice(title=_(u"Principal"), source="plone.principalsource.Principals"),
required=False,
missing_value=(), # important!
)
alsoProvides(IReviewers, form.IFormFieldProvider)
class IReviewersMarker(Interface):
"""Marker interface that will be provided by instances using the
IReviewers behavior. The ILocalRoleProvider adapter is registered for
this marker.
"""
class ReviewerLocalRoles(grok.Adapter):
"""Grant local roles to reviewers when the behavior is used.
"""
grok.implements(ILocalRoleProvider)
grok.context(IReviewersMarker)
grok.name('iz.behaviors.reviewers')
def getRoles(self, principal_id):
"""If the user is in the list of reviewers for this item, grant
the Reader, Editor and Contributor local roles.
"""
c = IReviewers(self.context, None)
if c is None or (not c.official_reviewers and not c.unofficial_reviewers):
return ()
if principal_id in c.official_reviewers:
return ('Reviewer', 'OfficialReviewer',)
elif principal_id in c.unofficial_reviewers:
return ('Reviewer',)
return ()
def getAllRoles(self):
"""Return a list of tuples (principal_id, roles), where roles is a
list of roles for the given user id.
"""
c = IReviewers(self.context, None)
if c is None or (not c.official_reviewers and not c.unofficial_reviewers):
return
seen = set ()
for principal_id in c.official_reviewers:
seen.add(principal_id)
yield (principal_id, ('Reviewer', 'OfficialReviewer'),)
for principal_id in c.unofficial_reviewers:
if principal_id not in seen:
yield (principal_id, ('Reviewer',),)
class ReviewersIndexer(grok.MultiAdapter):
"""Catalog indexer for the 'reviewers' index.
"""
grok.implements(IIndexer)
grok.adapts(IReviewersMarker, IZCatalog)
grok.name('reviewers')
def __init__(self, context, catalog):
self.reviewers = IReviewers(context)
def __call__(self):
official = self.reviewers.official_reviewers or ()
unofficial = self.reviewers.unofficial_reviewers or ()
return tuple(set(official + unofficial))
Note that the iz.EditOfficialReviewers and
iz.EditUnofficialReviewers permissions are defined and granted
elsewhere.
This is quite a complex behavior, but hopefully you can see what’s going
on:
- There is a standard schema interface, which is grokked for form hints
using plone.directives.form and marked as an IFormFieldProvider.
It uses plone.formwidget.autocomplete and plone.principalsource
to implement the fields.
- We define a marker interface (IReviewersMarker) and register this
with the marker attribute of the <plone:behavior /> directive.
- We define an adapter from this marker to ILocalRoles from
borg.localrole. Here, we have chosen to use grokcore.component
(via five.grok) to register the adapter. We could have used an
<adapter /> ZCML statement as well, of course.
- Similarly, we define a multi-adapter to IIndexer, as provided by
plone.indexer. Again, we’ve chosen to use
convention-over-configuration via five.grok to register this.
Although this behavior provides a lot of functionality, it is no more
difficult for integrators to use than any other: they would simply list
the behavior interface (iz.behaviors.reviewers.IReviewers in this
case) in the FTI, and all this functionality comes to life. This is the
true power of behaviors: developers can bundle up complex functionality
into re-usable behaviors, which can then be enabled on a per-type basis
by integrators (or the same developers in lazier moments).
