9. How to add a custom button to Django change view page?

Villain has a field called is_unique:

class Villain(Entity):
    ...
    is_unique = models.BooleanField(default=True)

You want to add a button on Villain change form page called “Make Unique”, which make this Villain unique. Any other villain with the same name should be deleted.

You start by extending the change_form to add a new button.:

{% extends 'admin/change_form.html' %}

{% block submit_buttons_bottom %}
    {{ block.super }}
    <div class="submit-row">
            <input type="submit" value="Make Unique" name="_make-unique">
    </div>
{% endblock %}

Then you can override response_change and connect your template to the VillainAdmin.:

@admin.register(Villain)
class VillainAdmin(admin.ModelAdmin, ExportCsvMixin):
    ...
    change_form_template = "entities/villain_changeform.html"


    def response_change(self, request, obj):
        if "_make-unique" in request.POST:
            matching_names_except_this = self.get_queryset(request).filter(name=obj.name).exclude(pk=obj.id)
            matching_names_except_this.delete()
            obj.is_unique = True
            obj.save()
            self.message_user(request, "This villain is now unique")
            return HttpResponseRedirect(".")
        return super().response_change(request, obj)

This is how your admin looks now.