• https://docs.djangoproject.com/en/3.0/ref/contrib/sites

Based on the Site class which its important attribute is domain that specifies the domain name of the site.

1. Add django.contrib.sites to your INSTALLED_APPS setting.
2. Define a SITE_ID setting: SITE_ID = 1
3. Run migrate.

django.contrib.sites registers a post_migrate signal handler which creates a default site named example.com with the domain example.com.

from django.contrib.sites.models import Site
from django.db import models
 
class Article(models.Model):
    headline = models.CharField(max_length=200)
    # ...
    sites = models.ManyToManyField(Site)
    # or: site = models.ForeignKey(Site, on_delete=models.CASCADE)
 
# ...
 
from django.contrib.sites.shortcuts import get_current_site
 
def article_detail(request, article_id):
    try:
        a = Article.objects.get(id=article_id, sites__id=get_current_site(request).id)
    except Article.DoesNotExist:
        raise Http404("Article does not exist on this site")
    # ...

from django.contrib.sites.shortcuts import get_current_site
# ...
current_site = get_current_site(request)

>>> from django.contrib.sites.models import Site
>>> obj = MyModel.objects.get(id=3)
>>> obj.get_absolute_url()
'/mymodel/objects/3/'
>>> Site.objects.get_current().domain
'example.com'
>>> 'https://%s%s' % (Site.objects.get_current().domain, obj.get_absolute_url())
'https://example.com/mymodel/objects/3/'

from django.conf import settings
 
def my_view(request):
    if settings.SITE_ID == 3:
        # Do something.
        pass
    else:
        # Do something else.
        pass

or…

from django.contrib.sites.shortcuts import get_current_site
 
def my_view(request):
    current_site = get_current_site(request)
    if current_site.domain == 'foo.com':
        # Do something
        pass
    else:
        # Do something else.
        pass

If you wanted to choose different templates refer to this link.