Question

We have a Django DetailView where we’re displaying an an object (Site), along with all of it’s related objects (Rooms).

Now, in the template, we could simply iterate over the RelatedManager set:

{% for room in site.room_set.all %}
    do stuff
{% endfor %}

However, the problem for this is that this will pick up all related rooms to a site – however, we need to narrow this set down somewhat by another attribute (let’s call it year) – and this attribute is stored in a Django session variable.

Currently, we’re just using Room.objects.filter(site=some_site, year='2009') in the view code, and that’s fine.

My question is more from curiosity – is there any way to use _set in the template, and still filter down or narrow the set?

Could you write a custom Model Manager to do this, so that _set will only ever return objects for the current year? Or is there some other way?

Cheers,
Victor

Answer 1

My question is more from curiosity – is there any way to use _set in
the template, and still filter down or narrow the set?

Not by default, since there’s no way to pass arguments to the filter call.

• If it’s functionality that needs to be repeated variably, often, and related to the template: build a custom template tag or filter (which can accept arguments).
• If it’s functionality that’s specific to a view, code it in the view.
• If it’s functionality that’s the same across multiple views, build the function in a dry place.

For #3, there are so many factors that determine where this code should go that there’s no general solution. You could import a function into your views? Use a model manager? A model instance method? context processor? etc.

Could you write a custom Model Manager to do this, so that _set will
only ever return objects for the current year? Or is there some other
way?

It looks like you can actually just by using a model manager for your reverse related model.

class RoomManager(models.Manager):
    def current_year(self):
        return self.get_queryset().filter(year=datetime.date.today().year)

for room in site.room_set.current_year():
   ...

Or just on the parent model:

class Site(models.Model):
    ...
    def year_room_set(self):
        return self.room_set.filter(year=datetime.date.today().year)