Question

We customized the News Item-type and replaced the embedded image with an ExtendedReferenceField (we use a central image repository).

Is there a way to activate link integrity checking on that field so that when one tries to delete the image a warning is triggered?

(Yes, link integrity checking is enabled in @@editing-controlpanel and works just fine when I insert links and images in the content body).

Condensed code for the schemaextender field used:

from zope.interface import implements
from archetypes.schemaextender.interfaces import ISchemaExtender
from archetypes.schemaextender.interfaces import IBrowserLayerAwareExtender
from archetypes.schemaextender.field import ExtensionField
from Products.Archetypes import atapi
from archetypes.referencebrowserwidget.widget import ReferenceBrowserWidget

class ExtendedReferenceField(ExtensionField, atapi.ReferenceField):
    """ Extention reference field. """

class ImageReferenceExtender(object):
    implements(ISchemaExtender, IBrowserLayerAwareExtender)

    layer = IPackageSpecific

    fields = [
        ExtendedReferenceField(
            name= 'imageref',
            required = False,
            multiValued=False,
            allowed_types=('Image', ),
            relationship='image',
            keepReferencesOnCopy=True,
            widget = ReferenceBrowserWidget(
                ...
                )),
    ]

    def __init__(self, context):
        self.context = context

    def getFields(self):
        return self.fields

This happens in Plone version 3.3.6 as well as 4.1.6.

Answer 1

Link integrity works by adding references named isReferencing between objects, but it only does this for HTML links within TextFields, whenever an object is modified.

To support individual reference fields, you have 2 options:

1. Add isReferencing relationships whenever you add your image relationship, remove them again when the image relationship is gone, using events or the extender. Link integrity will then kick in.

2. Track the removal of an image relationship as an integrity breach. You’d need to check if the referring object is being removed.

   Take a look at the handlers.py module of the plone.app.linkintegrity package. The referenceRemoved event handler is called whenever any Archetypes reference is deleted. It updates the ILinkIntegrityInfo storage, adding both source and target of a isReferencing relationship, and this storage is consulted when handling content object deletion.

   Create a new event handler for your image reference and it’ll be handled in the same way; delete a referenced image and the link integrity warning will be raised:

   from plone.app.linkintegrity.interfaces import ILinkIntegrityInfo
   from Products.Archetypes.interfaces import IReference
   from Acquisition import aq_get
   
   def imageReferenceRemoved(obj, event):
       assert IReference.providedBy(obj)
       assert obj is event.object # just making sure...
       if not obj.relationship == 'image':
           return
       # if the object the event was fired on doesn't have a `REQUEST` attribute
       # we can safely assume no direct user action was involved and therefore
       # never raise a link integrity exception...
       request = aq_get(obj, 'REQUEST', None)
       if not request:
           return
       storage = ILinkIntegrityInfo(request)
       storage.addBreach(obj.getSourceObject(), obj.getTargetObject())
   

   registered with ZCML:

    <configure xmlns="http://namespaces.zope.org/zope">
    <subscriber
        for="Products.Archetypes.interfaces.IReference
             zope.lifecycleevent.interfaces.IObjectRemovedEvent"
        handler=".events.imageReferenceRemoved"
        />
    </configure>