different_database_model.py

from django.db import models
from django.db.models import QuerySet

# The value is the key that goes in the `DATABASES` settings.
# Ideally set in the Django settings as well, so it can be project-wide accessible
SOURCE_DB_LABEL = 'source_db'

class SourceServiceQuerySet(QuerySet):
    def as_manager(cls):
        return super().as_manager().db_manager(SOURCE_DB_LABEL)
    as_manager.queryset_only = True
    as_manager = classmethod(as_manager)


class SourceServiceModel(models.Model):
    objects = SourceServiceQuerySet.as_manager()

    class Meta:
        abstract = True