Third-party applications support

django-reversion support

Support for django-reversion works as expected with polymorphic models. However, they require more setup than standard models. That’s become:

• The children models are not registered in the admin site. You will therefore need to manually register them to django-reversion.
• Polymorphic models use multi-table inheritance. See the reversion documentation how to deal with this by adding a follow field for the primary key.
• Both admin classes redefine object_history_template.

Example

The admin Example becomes:

from django.contrib import admin
from polymorphic.admin import PolymorphicParentModelAdmin, PolymorphicChildModelAdmin
from reversion.admin import VersionAdmin
from reversion import revisions
from .models import ModelA, ModelB, ModelC


class ModelAChildAdmin(PolymorphicChildModelAdmin, VersionAdmin):
    base_model = ModelA
    base_form = ...
    base_fieldsets = (
        ...
    )

class ModelBAdmin(ModelAChildAdmin, VersionAdmin):
    # define custom features here

class ModelCAdmin(ModelBAdmin):
    # define custom features here


class ModelAParentAdmin(VersionAdmin, PolymorphicParentModelAdmin):
    base_model = ModelA
    child_models = (
        (ModelB, ModelBAdmin),
        (ModelC, ModelCAdmin),
    )

revisions.register(ModelB, follow=['modela_ptr'])
revisions.register(ModelC, follow=['modelb_ptr'])
admin.site.register(ModelA, ModelAParentAdmin)

Redefine a admin/polymorphic/object_history.html template, so it combines both worlds:

{% extends 'reversion/object_history.html' %}
{% load polymorphic_admin_tags %}

{% block breadcrumbs %}
    {% breadcrumb_scope base_opts %}{{ block.super }}{% endbreadcrumb_scope %}
{% endblock %}

This makes sure both the reversion template is used, and the breadcrumb is corrected for the polymorphic model.

django-reversion-compare support

The django-reversion-compare views work as expected, the admin requires a little tweak. In your parent admin, include the following method:

def compare_view(self, request, object_id, extra_context=None):
    """Redirect the reversion-compare view to the child admin."""
    real_admin = self._get_real_admin(object_id)
    return real_admin.compare_view(request, object_id, extra_context=extra_context)

As the compare view resolves the the parent admin, it uses it’s base model to find revisions. This doesn’t work, since it needs to look for revisions of the child model. Using this tweak, the view of the actual child model is used, similar to the way the regular change and delete views are redirected.

django-mptt support

Combining polymorphic with django-mptt is certainly possible, but not straightforward. It involves combining both managers, querysets, models, meta-classes and admin classes using multiple inheritance.

The django-polymorphic-tree package provides this out of the box.