python - Fastest way to get the first object from a queryset in django?

Question

Often I find myself wanting to get the first object from a queryset in Django, or return None if there aren't any. There are lots of ways to do this which all work. But I'm wondering which is the most performant.

qs = MyModel.objects.filter(blah = blah)
if qs.count() > 0:
    return qs[0]
else:
    return None

Does this result in two database calls? That seems wasteful. Is this any faster?

qs = MyModel.objects.filter(blah = blah)
if len(qs) > 0:
    return qs[0]
else:
    return None

Another option would be:

qs = MyModel.objects.filter(blah = blah)
try:
    return qs[0]
except IndexError:
    return None

This generates a single database call, which is good. But requires creating an exception object a lot of the time, which is a very memory-intensive thing to do when all you really need is a trivial if-test.

How can I do this with just a single database call and without churning memory with exception objects?

Answer 1

Use the convenience methods .first() and .last():

MyModel.objects.filter(blah=blah).first()

They both swallow the resulting exception and return None if the queryset returns no objects.

These were added in Django 1.6, which was released in Nov 2013.