Admin Integration
-----------------

To allow viewing previous model versions on the Django admin site, inherit from
the ``simple_history.admin.SimpleHistoryAdmin`` class when registering your
model with the admin site.

This will replace the history object page on the admin site and allow viewing
and reverting to previous model versions.  Changes made in admin change forms
will also accurately note the user who made the change.

.. image:: screens/1_poll_history.png

Clicking on an object presents the option to revert to that version of the object.

.. image:: screens/2_revert.png

(The object is reverted to the selected state)

.. image:: screens/3_poll_reverted.png

Reversions like this are added to the history.

.. image:: screens/4_history_after_poll_reverted.png

An example of admin integration for the ``Poll`` and ``Choice`` models:

.. code-block:: python

    from django.contrib import admin
    from simple_history.admin import SimpleHistoryAdmin
    from .models import Poll, Choice

    admin.site.register(Poll, SimpleHistoryAdmin)
    admin.site.register(Choice, SimpleHistoryAdmin)

Changing a history-tracked model from the admin interface will automatically record the user who made the change (see :doc:`/user_tracking`).


Displaying custom columns in the admin history list view
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

By default, the history log displays one line per change containing

* a link to the detail of the object at that point in time
* the date and time the object was changed
* a comment corresponding to the change
* the author of the change

You can add other columns (for example the object's status to see
how it evolved) by adding a ``history_list_display`` array of fields to the
admin class.

.. code-block:: python

    from django.contrib import admin
    from simple_history.admin import SimpleHistoryAdmin
    from .models import Poll, Choice


    class PollHistoryAdmin(SimpleHistoryAdmin):
        list_display = ["id", "name", "status"]
        history_list_display = ["status"]
        search_fields = ['name', 'user__username']
        history_list_per_page = 100

    admin.site.register(Poll, PollHistoryAdmin)
    admin.site.register(Choice, SimpleHistoryAdmin)


.. image:: screens/5_history_list_display.png


Changing the page size in the admin history list view
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

By default, the history list view of ``SimpleHistoryAdmin`` shows the last 100 records.
You can change this by adding a `history_list_per_page` attribute to the admin class.


.. code-block:: python

    from django.contrib import admin
    from simple_history.admin import SimpleHistoryAdmin
    from .models import Poll


    class PollHistoryAdmin(SimpleHistoryAdmin):
        # history_list_per_page defaults to 100
        history_list_per_page = 200

    admin.site.register(Poll, PollHistoryAdmin)


Customizing the History Admin Templates
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you'd like to customize the HTML of ``SimpleHistoryAdmin``'s object history pages,
you can override the following attributes with the names of your own templates:

- ``object_history_template``: The main object history page, which includes (inserts)
  ``object_history_list_template``.
- ``object_history_list_template``: The table listing an object's historical records and
  the changes made between them.
- ``object_history_form_template``: The form pre-filled with the details of an object's
  historical record, which also allows you to revert the object to a previous version.

If you'd like to only customize certain parts of the mentioned templates, look for
``block`` template tags in the source code that you can override - like the
``history_delta_changes`` block in ``simple_history/object_history_list.html``,
which lists the changes made between each historical record.

Customizing Context
^^^^^^^^^^^^^^^^^^^

You can also customize the template context by overriding the following methods:

- ``render_history_view()``: Called by both ``history_view()`` and
  ``history_form_view()`` before the templates are rendered. Customize the context by
  changing the ``context`` parameter.
- ``history_view()``: Returns a rendered ``object_history_template``.
  Inject context by calling the super method with the ``extra_context`` argument.
- ``get_historical_record_context_helper()``: Returns an instance of
  ``simple_history.template_utils.HistoricalRecordContextHelper`` that's used to format
  some template context for each historical record displayed through ``history_view()``.
  Customize the context by extending the mentioned class and overriding its methods.
- ``history_form_view()``: Returns a rendered ``object_history_form_template``.
  Inject context by calling the super method with the ``extra_context`` argument.


Disabling the option to revert an object
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

By default, an object can be reverted to its previous version. To disable this option
globally, update your settings with the following:

.. code-block:: python

    SIMPLE_HISTORY_REVERT_DISABLED = True

When ``SIMPLE_HISTORY_REVERT_DISABLED`` is set to ``True``, the revert button is removed from the form.

.. image:: screens/10_revert_disabled.png

Enforcing history model permissions in Admin
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

To make the Django admin site evaluate history model permissions explicitly,
update your settings with the following:

.. code-block:: python

    SIMPLE_HISTORY_ENFORCE_HISTORY_MODEL_PERMISSIONS = True

By default, ``SIMPLE_HISTORY_ENFORCE_HISTORY_MODEL_PERMISSIONS`` is set to ``False``.
When set to ``False``, permissions applied to the ``Poll`` model
(from the examples above), also apply to the history model.
That is, granting view and change permissions to the ``Poll`` model
implicitly grants view and change permissions to the ``Poll`` history model.

The user below has view and change permissions to the ``Poll`` model and the ``Poll``
history model in admin.

.. code-block:: python

    user.user_permissions.clear()
    user.user_permissions.add(
        Permission.objects.get(codename="view_poll"),
        Permission.objects.get(codename="change_poll"),
    )

The user below has view permission to the ``Poll`` model and the ``Poll`` history model
in admin.

.. code-block:: python

    user.user_permissions.clear()
    user.user_permissions.add(
        Permission.objects.get(codename="view_poll"),
    )

When ``SIMPLE_HISTORY_ENFORCE_HISTORY_MODEL_PERMISSIONS`` is set to ``True``,
permissions to history models are assigned and evaluated explicitly.

The user below *does not have* view permission to the ``Poll`` history model in admin,
even though they *have* view permission to the ``Poll`` model.

.. code-block:: python

    # SIMPLE_HISTORY_ENFORCE_HISTORY_MODEL_PERMISSIONS = True in settings
    user.user_permissions.clear()
    user.user_permissions.add(
        Permission.objects.get(codename="view_poll"),
    )

The user below has view permission to the ``Poll`` model and the ``Poll``
history model.

.. code-block:: python

    # SIMPLE_HISTORY_ENFORCE_HISTORY_MODEL_PERMISSIONS = True in settings
    user.user_permissions.clear()
    user.user_permissions.add(
        Permission.objects.get(codename="view_poll"),
        Permission.objects.get(codename="view_historicalpoll"),
    )

The user below has view permission to the ``Poll`` history model, but will need to
access the page with a direct URL, since the ``Poll`` model will not be listed on
the admin application index page, nor the ``Poll`` changelist.

.. code-block:: python

    # SIMPLE_HISTORY_ENFORCE_HISTORY_MODEL_PERMISSIONS = True in settings
    user.user_permissions.clear()
    user.user_permissions.add(
        Permission.objects.get(codename="view_historicalpoll"),
    )