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?
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.