django conditionally filtering objects

Question

I would like to retrieve a bunch of rows from my database using a set of filters.

I was wondering if conditional filter is applicable in django. That is, "filter if variable is not None, or not apply filtering otherwise".

Something like this:

user = User.objects.get(pk=1)
category = Category.objects.get(pk=1)
todays_items = Item.objects.filter(user=user, date=now()).conditional_filter(category=category))

What I would like to do is apply category filter only if category is not None.

If category is None (means it is not given in the request object) then this filter would not be applied at all. This would save me a bunch of 'if-elif-else' situations.

Is there a way to do this?

Answer 1

You can chain queries:

user = User.objects.get(pk=1)
category = Category.objects.get(pk=1)
qs = Item.objects.filter(user=user, date=now())
if category:
    qs = qs.filter(category=category)

As queryset are executed lazily, DB hit will occur only when you display items.