Django model `get` does not return false

Question

I have an Django app which check if the the database holds numbers which matches the numbers entered by the user in the form. I've managed to get it to redirect to the 'You win' page if they do match but when they don't match it just gives an error saying 'matching query does not exist.' Here's the if/else statement I'm using in the view.py file:

if Numbers.objects.get(numbers_win = user_number):
     return HttpResponseRedirect('win')
else:
     return HttpResponseRedirect('lose.html')

What does `Numbers.object.get..` returns ? Are you sure it returns a boolean ? — Mel, Jan 08 '16 at 12:47
Maybe this will help: http://stackoverflow.com/questions/3090302/in-django-how-do-i-objects-get-but-return-none-when-nothing-is-found So you would have to surround it with try except instead of if. — allu, Jan 08 '16 at 12:47

score 6 · Answer 1 · edited Jan 08 '16 at 13:03

6

That's because .get throws an exception when there are no matches — it doesn't return something falsey.

You have two options:

First, you can use filter and existsinstead of get, which will return True if something is found, and False otherwise.

If you're not otherwise using the result, this is probably the best solution:

if Numbers.objects.filter(numbers_win = user_number).exists():
     return HttpResponseRedirect('win')
else:
     return HttpResponseRedirect('lose.html')

(As noted in the comments, using exists is faster if you're just checking for existence)

Second, you could catch the exception instead of using if / else:

try:
    Numbers.objects.get(numbers_win = user_number)
except Numbers. DoesNotExist:
    return HttpResponseRedirect('lose.html')
else:  
    return HttpResponseRedirect('win')

As you can see, though, this makes for somewhat awkward code, and it also performs worse than using .exists, so you probably shouldn't do this.

edited Jan 08 '16 at 13:03

jpic

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answered Jan 08 '16 at 12:48

Thomas Orozco

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Actually, OP should use `.filter(...).exists()` if all they want to do is verify the item is in the db. – Daniel Roseman Jan 08 '16 at 12:50
Thanks @DanielRoseman; corrected – Thomas Orozco Jan 08 '16 at 12:54
It will perform better if you assign the result of the get call in a variable and use it in the else statement though, which is probably what the user wants to do. – jpic Jan 08 '16 at 13:02
@jpic Sure; this is what the "if you're not otherwise using the result" note addresses (in the question, they're not actually using the result of the `get` call). – Thomas Orozco Jan 08 '16 at 13:07
Thank you! That does make a lot of sense. – CNB Jan 08 '16 at 13:09

Django model `get` does not return false

1 Answers1