How to choose a Wagtail image across a ParentalManyToManyField? - django

Question

Environment:
Wagtail 1.13
Django Version: 1.11.11
Python Version: 2.7.12
I'm following the Wagtail documentation to try to add an image showcase (not a category) to a page using ParentalManyToManyField:
class HomePage(Page):
showcase_title = models.CharField(max_length=100, blank="true", default="SHOWCASE")
showcase_images = ParentalManyToManyField('wagtailimages.Image')
content_panels = Page.content_panels + [
FieldPanel('showcase_title'),
InlinePanel('showcase_images', label="Showcase images", panels=[
ImageChooserPanel('showcase_images')
]),
]
Everything is fine if I comment out the showcase_images editing panel, but I get a KeyError as soon as uncomment the panel showcase_images. In addition to the above variation of editing showcase_images, I've also tried simply InlinePanel('showcase_images'), FieldPanel('showcase_images'), InlinePanel('showcase_images', label="Showcase images", panels=[ImageChooserPanel('image')]), and probably another variation or two. Can someone propose a solution?
Environment:
Request Method: GET
Request URL: http://dev.somedomain.com:8181/admin/pages/3/edit/
Django Version: 1.11.11
Python Version: 2.7.12
Installed Applications:
[u'my_app',
u'search',
u'wagtail.wagtailforms',
u'wagtail.wagtailredirects',
u'wagtail.wagtailembeds',
u'wagtail.wagtailsites',
u'wagtail.wagtailusers',
u'wagtail.wagtailsnippets',
u'wagtail.wagtaildocs',
u'wagtail.wagtailimages',
u'wagtail.wagtailsearch',
u'wagtail.wagtailadmin',
u'wagtail.wagtailcore',
u'wagtail.contrib.wagtailstyleguide',
u'modelcluster',
u'taggit',
u'wagtailfontawesome',
u'django.contrib.admin',
u'django.contrib.auth',
u'django.contrib.contenttypes',
u'django.contrib.sessions',
u'django.contrib.messages',
u'django.contrib.staticfiles']
Installed Middleware:
[u'django.contrib.sessions.middleware.SessionMiddleware',
u'django.middleware.common.CommonMiddleware',
u'django.middleware.csrf.CsrfViewMiddleware',
u'django.contrib.auth.middleware.AuthenticationMiddleware',
u'django.contrib.messages.middleware.MessageMiddleware',
u'django.middleware.clickjacking.XFrameOptionsMiddleware',
u'django.middleware.security.SecurityMiddleware',
u'wagtail.wagtailcore.middleware.SiteMiddleware',
u'wagtail.wagtailredirects.middleware.RedirectMiddleware']
Traceback:
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/django/core/handlers/exception.py" in inner
41. response = get_response(request)
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/django/core/handlers/base.py" in _get_response
187. response = self.process_exception_by_middleware(e, request)
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/django/core/handlers/base.py" in _get_response
185. response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/django/views/decorators/cache.py" in _cache_controlled
43. response = viewfunc(request, *args, **kw)
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/wagtail/wagtailadmin/urls/__init__.py" in wrapper
96. return view_func(request, *args, **kwargs)
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/wagtail/wagtailadmin/decorators.py" in decorated_view
31. return view_func(request, *args, **kwargs)
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/wagtail/wagtailadmin/views/pages.py" in edit
481. edit_handler = edit_handler_class(instance=page, form=form)
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/wagtail/wagtailadmin/edit_handlers.py" in __init__
269. self.children.append(child(instance=self.instance, form=self.form))
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/wagtail/wagtailadmin/edit_handlers.py" in __init__
269. self.children.append(child(instance=self.instance, form=self.form))
File "/opt/virtualenvs/gmmiTMID/lib/python2.7/site-packages/wagtail/wagtailadmin/edit_handlers.py" in __init__
693. self.formset = form.formsets[self.__class__.relation_name]
Exception Type: KeyError at /admin/pages/3/edit/
Exception Value: u'showcase_images'

Answer 1

InlinePanel doesn't work with ParentalManyToManyField relations, only ParentalKey relations. You'll need to set up an intermediate model to define the relation between pages and images, like BlogPageGalleryImage in the tutorial's 'images' section (but with the caption field omitted in this case, so it's just a direct association between pages and images).
(Alternatively, you can use a plain FieldPanel with ParentalManyToManyField, but this will just give you a set of checkboxes for all images in the system, rather than the the image chooser interface.)