Django: Dynamically set SITE_ID in settings.py based on URL?

You can do a custom middleware which reads the request and sets the SITE_ID. I use this code on one of my sites:

class SiteMiddleware(object):
    def process_request(self, request):
        try:
            current_site = Site.objects.get(domain=request.get_host())
        except Site.DoesNotExist:
            current_site = Site.objects.get(id=settings.DEFAULT_SITE_ID)

        request.current_site = current_site
        settings.SITE_ID = current_site.id

You should look at Django's documentation on middleware to find out how to add your own middleware. https://docs.djangoproject.com/en/dev/topics/http/middleware/

The middleware code form seems to have changed. The current (Django v3.1) form of the code (that seems to work):

from django.conf import settings
from django.contrib.sites.models import Site

class DynamicSiteDomainMiddleware:

    def __init__(self, get_response):
        self.get_response = get_response
        # One-time configuration and initialization.

    def __call__(self, request):
        try:
            current_site = Site.objects.get(domain=request.get_host())
        except Site.DoesNotExist:
            current_site = Site.objects.get(id=settings.DEFAULT_SITE_ID)

        request.current_site = current_site
        settings.SITE_ID = current_site.id


        response = self.get_response(request)
        return response