Computed Field on RichText

Plone Support Add-on Development
3

I have a behavior with a RichText field that displays the backreferences to site editors. i.e. not stored on the content object.

The field is only displayed in edit mode (as a temporaty workaround) to mitigate my inability to display it in view mode in a separate tab, see this post: Tabbed view for default CT

@provider(IFormFieldProvider)
class IBackReferences(model.Schema):
    """ 
    """
    model.fieldset(
        'backreferences',
        label=_(u'Back References'),
        fields=[
            'backreferences'
        ]
    )

    backreferences = RichText(
        title=_(u'Back References'),
        description=_(u''),
        required=False,
        #readonly=True,
    )
    form.mode(IEditForm, backreferences='display')

and

@implementer(IBackReferences)
@adapter(IBackReferencesMarker)
class BackReferences(object):
    
    def __init__(self, context):
        self.context = context

    @property
    def backreferences(self):
        relationvalues = get_referers_list(self.context, True)
        brains = get_brains_for_relation_ids(self.context, relationvalues, sort_key='Title')
        html_result_list = ['<li><a href="%s">%s</a></li>' % (brain.getURL(), brain.Title) for brain in brains]
        return Markup(u'<ul>%s</ul>' % '\n'.join(html_result_list))

The edit view shows my backreferences for existing content. But editors can not add new content, plone fails with the second traceback.

If I use the @ComputedAttribute decorator on backreferences then content can be added but when the document is edited again, Plone fails with the first traceback.

I have other use cases where this approach does work. I just realize that there is no field named "image" in that behavior...

    @ComputedAttribute
    def image(self):
        image_link = getattr(self.context.aq_explicit, 'related_image', False)
        linked_image = image_link and self.context.related_image.to_object.image or ''
        return linked_image