ComponentLookupError: (<InterfaceClass zc.relation.interfaces.ICatalog>, '') with Dexterity references - reference

Question

The following is a snippet from a dexterity content type which I'm working on. There are two content types, Programmes and Projects. It should be possible to associate a Project with a Programme (I've defined that below as a RelationChoice).
from five import grok
from plone.directives import dexterity, form
from zope import schema
from zope.schema.interfaces import IContextSourceBinder
from zope.schema.vocabulary import SimpleVocabulary, SimpleTerm
from zope.interface import invariant, Invalid
from z3c.form import group, field
from plone.namedfile.interfaces import IImageScaleTraversable
from plone.namedfile.field import NamedImage, NamedFile
from plone.namedfile.field import NamedBlobImage, NamedBlobFile
from plone.app.textfield import RichText
from z3c.relationfield.schema import RelationList, RelationChoice
from plone.formwidget.contenttree import ObjPathSourceBinder
from alteroo.programmeshowcase import MessageFactory as _
from alteroo.programmeshowcase.project import IProject
# Interface class; used to define content-type schema.
class IBaseProgramme(form.Schema, IImageScaleTraversable):
"""
Programme
"""
# If you want a schema-defined interface, delete the form.model
# line below and delete the matching file in the models sub-directory.
# If you want a model-based interface, edit
# models/progamme.xml to define the content type
# and add directives here as necessary.
form.model("models/programme.xml")
class IProgamme(IBaseProgramme):
"""A conference program. Programs can contain Sessions.
"""
project = RelationChoice(
title=_(u"Project"),
source=ObjPathSourceBinder(object_provides=IProject.__identifier__),
required=False,
)
The definition above results in an editing view that looks like this. When I try to add a related project it throws an error.
Here's the traceback I get when I try to add a related project:
Traceback (innermost last):
Module ZPublisher.Publish, line 126, in publish
Module ZPublisher.mapply, line 77, in mapply
Module ZPublisher.Publish, line 46, in call_object
Module plone.z3cform.layout, line 66, in __call__
Module plone.z3cform.layout, line 50, in update
Module plone.dexterity.browser.add, line 112, in update
Module plone.z3cform.fieldsets.extensible, line 59, in update
Module plone.z3cform.patch, line 30, in GroupForm_update
Module z3c.form.group, line 141, in update
Module plone.app.z3cform.csrf, line 21, in execute
Module z3c.form.action, line 98, in execute
Module z3c.form.button, line 315, in __call__
Module z3c.form.button, line 170, in __call__
Module plone.dexterity.browser.add, line 99, in handleAdd
Module z3c.form.form, line 247, in createAndAdd
Module plone.dexterity.browser.add, line 78, in add
Module plone.dexterity.utils, line 167, in addContentToContainer
Module OFS.ObjectManager, line 358, in _setObject
Module zope.event, line 31, in notify
Module zope.component.event, line 24, in dispatch
Module zope.component._api, line 136, in subscribers
Module zope.component.registry, line 321, in subscribers
Module zope.interface.adapter, line 585, in subscribers
Module zope.component.event, line 32, in objectEventNotify
Module zope.component._api, line 136, in subscribers
Module zope.component.registry, line 321, in subscribers
Module zope.interface.adapter, line 585, in subscribers
Module five.intid.intid, line 101, in addIntIdSubscriber
Module zope.event, line 31, in notify
Module zope.component.event, line 24, in dispatch
Module zope.component._api, line 136, in subscribers
Module zope.component.registry, line 321, in subscribers
Module zope.interface.adapter, line 585, in subscribers
Module z3c.relationfield.event, line 39, in addRelationsEventOnly
Module z3c.relationfield.event, line 28, in addRelations
Module z3c.relationfield.event, line 143, in _setRelation
Module zope.component._api, line 169, in getUtility
ComponentLookupError: (<InterfaceClass zc.relation.interfaces.ICatalog>, '')

Answer 1

You need to activate "Relation Field" (plone.app.relationfield) in the Addons control panel to install the relation catalog.