It’s worth noting that the
QuerySet.values_list() method doesn’t actually return a list, but an object of type
django.db.models.query.ValuesListQuerySet, in order to maintain Django’s goal of lazy evaluation, i.e. the DB query required to generate the ‘list’ isn’t actually performed until the object is evaluated.
Somewhat irritatingly, though, this object has a custom
__repr__ method which makes it look like a list when printed out, so it’s not always obvious that the object isn’t really a list.
The exception in the question is caused by the fact that custom objects cannot be serialized in JSON, so you’ll have to convert it to a list first, with…
my_list = list(self.get_queryset().values_list('code', flat=True))
…then you can convert it to JSON with…
json_data = json.dumps(my_list)
You’ll also have to place the resulting JSON data in an
HttpResponse object, which, apparently, should have a
response = HttpResponse(json_data, content_type='application/json')
…which you can then return from your function.