django and sites framework chaining in relationships

Question

A little question about one of the most useful django frameworks:

django.contrib.sites

Assuming I have a model:

class MyModel(models.Model):
    info = models.TextField()
    site = models.ManyToManyField(Site)
    objects = models.Manager()
    on_site = CurrentSiteManager()

and another model, that's linked to the given above:

class MyModelSupplement(models.Model):
    info = models.TextField()
    parent_model = models.ForeignKey(MyModel)

Scheme specifies, that MyModelSupplement can't belong to sites, it's parent doesn't belong to.

having this structure I can access MyModel object on the given site simply by invoking

MyModel.on_site.all()

code. What's the best way to achieve the same on MyModelSupplement model?

I can think of a few ways to solve this:

1. putting the same site field in MyModelSupplement and defining the same CurrentSiteManager (won't that be a bit redundant?)
2. use MyModelSupplement.objects.filter(parent_model__site__id = some_site_id)
3. MyModel.on_site.all().values_list('mymodelsupplement')
4. Or even go to this variant:

 my_models = MyModel.on_site.all()       \nmy_models_supplements = MyModelSupplements.objects.filter(parent_model__in=my_models).select_related()  

is there a better way of accomplishing the mentioned task? The note is that I need to access both this models both together and separately, trying to retrieve instances respected to the given site?

Maybe there's a way to say something like: all SiteID values from MyModel should be in MyModelSupplement . If SiteID value was deleted from MyModel instance, it should be deleted from all MyModelSupplements , that are related to the the respected MyModel instance with ManyToMany relationship.

Is that achievable?

Answer 1

I was able to solve this problem the following way:

this goes before everything happens:

from django.conf import settings

after that, we create a custom manager:

class OnSiteMyModelSupplementManager(models.Manager):
    def get_query_set(self):
        return super(OnSiteMyModelSupplementManager, self).get_query_set().filter(parent_model__sites=settings.SITE_ID)

and simply putting two more lines of code into MyModelSupplement class:

objects = models.Manager()
on_site = OnSiteMyModelSupplementManager()

and now I'm capable of retrieving MyModelSupplements, that belong only to the current web-site, as there parents do.