How to add the custom button which executes a Django admin action to change form page?

Question

I have already defined a custom admin action for my model which works perfectly as expected. I also looked at multiple ways of adding a button to the admin change form page here on SO. The only step that I am missing is how do I make a button in the change form page execute my custom admin action with current object?

The goal is to allow admin to inspect every object individually and perform an action on them without needing to go back to list view, selecting the inspected object, and executing the action from the list.

My custom admin action looks like this:

def admin_apply_change(modeladmin, request, queryset):
    # loop over objects in query set and perform action

I am assuming there is a simple and clean way of calling this action in admin change form, where the queryset would only contain the currently opened object the admin is looking at.

NOTE: It would be preferable if the button is at the bottom of the change form, next to Save button instead of being at top with History which is not very visible.

Solution:

See the answer below by Remi for the solution. In order to make it work the following corrections are needed:

1. In the override of response_change initialization of some variables is missing:

   opts = self.model._meta
   pk_value = obj._get_pk_val()
   preserved_filters = self.get_preserved_filters(request)
   

2. New inclusion tag custom_submit_row should be placed in templatetags and not in admin (see docs for custom templatetags)

3. This is the oversight you could lose some time on. In change_form.html you not only have to change the suggested line:

   {% if save_on_top %}{% block submit_buttons_top %}{% submit_row %}{% endblock %}{% endif %}
   

   but also the more important line at the bottom where submit_row appears:

   {% block submit_buttons_bottom %}{% submit_row %}{% endblock %}
   

   It is located just above the javascript block in change_form.html.

Answer 1

You could take a look at the change_form_template and set it to a custom template of yours and override the response_change method:

class MyModelAdmin(admin.ModelAdmin):

    # A template for a customized change view:
    change_form_template = 'path/to/your/custom_change_form.html'

    def response_change(self, request, obj):
        opts = self.model._meta
        pk_value = obj._get_pk_val()
        preserved_filters = self.get_preserved_filters(request)

        if "_customaction" in request.POST:
            # handle the action on your obj
            redirect_url = reverse('admin:%s_%s_change' %
                               (opts.app_label, opts.model_name),
                               args=(pk_value,),
                               current_app=self.admin_site.name)
             redirect_url = add_preserved_filters({'preserved_filters': preserved_filters, 'opts': opts}, redirect_url)
             return HttpResponseRedirect(redirect_url)
        else:
             return super(MyModelAdmin, self).response_change(request, obj)

Copy the change_form.html from your site-packages/django/contrib/admin/templates/change_form.html and edit the line 40

 {% if save_on_top %}{% block submit_buttons_top %}{% submit_row %}{% endblock %}{% endif %}

to

 {% if save_on_top %}{% block submit_buttons_top %}{% custom_submit_row %}{% endblock %}{% endif %}

Also check the line:

 {% block submit_buttons_bottom %}{% submit_row %}{% endblock %}

just above the javascript block.

Then you can register a new inclusion tag somewhere in your admin.py or add it to templatetags:

@register.inclusion_tag('path/to/your/custom_submit_line.html', takes_context=True)
def custom_submit_row(context):
    """
    Displays the row of buttons for delete and save.
    """
    opts = context['opts']
    change = context['change']
    is_popup = context['is_popup']
    save_as = context['save_as']
    ctx = {
        'opts': opts,
        'show_delete_link': (
            not is_popup and context['has_delete_permission'] and
            change and context.get('show_delete', True)
        ),
        'show_save_as_new': not is_popup and change and save_as,
        'show_save_and_add_another': (
            context['has_add_permission'] and not is_popup and
            (not save_as or context['add'])
        ),
        'show_save_and_continue': not is_popup and context['has_change_permission'],
        'is_popup': is_popup,
        'show_save': True,
        'preserved_filters': context.get('preserved_filters'),
    }
    if context.get('original') is not None:
        ctx['original'] = context['original']
    return ctx

The contents of your custom_submit_line.html:

{% load i18n admin_urls %}
<div class="submit-row">
{% if show_save %}<input type="submit" value="{% trans 'Save' %}" class="default" name="_save" />{% endif %}
{% if show_delete_link %}
    {% url opts|admin_urlname:'delete' original.pk|admin_urlquote as delete_url %}
    <p class="deletelink-box"><a href="{% add_preserved_filters delete_url %}" class="deletelink">{% trans "Delete" %}</a></p>
{% endif %}
{% if show_save_as_new %}<input type="submit" value="{% trans 'Save as new' %}" name="_saveasnew" />{% endif %}
{% if show_save_and_add_another %}<input type="submit" value="{% trans 'Save and add another' %}" name="_addanother" />{% endif %}
{% if show_save_and_continue %}<input type="submit" value="{% trans 'Save and continue editing' %}" name="_continue" />{% endif %}

<input type="submit" value="{% trans 'Custom Action' %}"  name="_customaction" />

</div>

It is a lot of code, but mostly copy/paste. Hope that helps.