[Fixed]-How can I get the Django admin's "View on site" link to work?

Define a get_absolute_url on your model. The admin uses that method to figure out how to construct the objects url. See the docs.

As communicated by others, this requires a couple extra steps in addition to enabling view_on_site. You have to implement get_absolute_url() in your model, and enable Sites in your project settings.

Set the view_on_site setting

Add view_on_site setting to admin form:

class MymodelAdmin(admin.ModelAdmin):
    ...
    view_on_site = True
...
admin.site.register(Mymodel, MymodelAdmin)

Implement get_absolute_url()

Add get_absolute_url() to your model.
In models.py:

Mymodel(models.Model):
    ...
    def get_absolute_url(self):
        return "/mystuff/%i" % self.id

Enable Sites

Add Sites in yourapp/settings.py:

INSTALLED_APPS = (
    ...
    'django.contrib.sites',
    ...
)

Then update the database:

$ python manage.py migrate

Done!

Check out reverse() for a more sophisticated way to generate the path in get_absolute_url().

According to the Django documentation, and as of Django 3.1 (May 2020), you have to define a get_absolute_url() method in your model.

One place Django uses get_absolute_url() is in the admin app. If an
object defines this method, the object-editing page will have a “View
on site” link that will jump you directly to the object’s public view,
as given by get_absolute_url().

Here is an example from the documentation:

def get_absolute_url(self):
        from django.urls import reverse
        return reverse('people.views.details', args=[str(self.id)])

Source: https://docs.djangoproject.com/en/3.1/ref/models/instances/#get-absolute-url

It seems to me that the view on site functionality works only if get_absolute_url refares to a Django view. It does not seem to work if you are trying to create a link, which redirects to a page out of Django’s control (even if it is served from the same domain by apache itself).

In this case, it is easy to create the button manually by overriding admin tempale as follows:

{% extends "admin/change_form.html" %}
{% block object-tools-items %}
{{ block.super }}
  <li>
    <a class="viewsitelink" href="{{ original.get_absolute_url }}">View on my site, out of Django's control</a>
  </li>
{% endblock %}

Also, add view_on_site = False to your ModelAdmin class, otherwise both of the buttons will appear.

When you have edited either SITE_ID in settings.py or a Site instance thought the admin, don’t forget to restart your web server for the change to take effect.