Question

Disclaimer: I am new to python and Django, but have Drupal programming experience.

I’m following the tutorials here (http://www.djangobook.com/en/2.0/chapter05/), but I’m confused by

Publisher.objects.filter(name='Apress')
[<Publisher: Apress>]

I understand that the result is a Queryset Object, so how can I retrieve the address (or primary key) when the following approach fails?

p = Publisher.objects.filter(name='Apress')
a = p.address
'QuerySet' object has no attribute 'address'

Thanks!

Answer 1

The attributes are only available on the model instances. A QuerySet is simplistically just as list of model instances, so you have to “unpack” it somehow to get at a particular instance and then the attribute on that.

If you know that there’s only one of the thing you’re querying for, you should use get instead of filter:

publisher = Publisher.objects.get(name='Apress')
print publisher.address

But, if multiple matches are returned, it will raise a MultipleObjectsReturned exception, and conversely, if no match is found an ObjectDoesNotExist exception is raised. As a result, you need to be careful when using get and make sure to wrap your code in appropriate try...except blocks.

If you’re dealing with something where you expect more than one result, then you can either use some sort of loop structure to deal with each individual item in the QuerySet:

for publisher in Publisher.objects.all():
    print publisher.address

Or, directly pull out one item as you would with a traditional list:

first_publisher = Publisher.objects.all()[0]
print first_publisher.address