How to prefix a foreign key object to a model field in Wagtail admin?

Question

In this case, each feature has one Epic (models.Model)

epic = models.ForeignKey(Epic, on_delete=models.CASCADE, default='')

In the admin drop-down (and only there) I would like to show each item as:

epic.name - feature.name

Because some of my features have a similar name but different epics. I can't change the __ str __ function of the Feature model or it will affect the whole app.

How can I achieve that?

Answer 1

One way to do this is to subclass Django's ModelChoiceField, and override the label_from_instance method that provides the label:

from django.forms import ModelChoiceField

class FeatureChoiceField(ModelChoiceField):
    def label_from_instance(self, obj):
        return "%s - %s" % (obj.epic.name, obj.name)

You'll then need to customise the edit form to use that custom form field type in place of the default ModelChoiceField:

from wagtail.admin.forms import WagtailAdminModelForm
# note - use WagtailAdminPageForm if this is a page model rather than a
# plain Django model managed through snippets / ModelAdmin

class ScopeForm(WagtailAdminModelForm):
    feature = FeatureChoiceField(queryset=Feature.objects.all())


class Scope(models.Model):
    # ...

    base_form_class = ScopeForm