— 1 min read

[] is not JSON serializable (django).

Serializing Django values_list.

Not very explicit error, especially if you re trying to serialize Django values_list.

data = MyModel.object.all().values_list('id', flat=true)

This indeed returns a list: [‘1’, '2’, '3’, …], So if you intend to serialize it you’ll likely get errors; that it’s not serializable.

This is actually not quite the full story. Because you are trying to serialize a ValuesListQuerySet and not a List.

type(data) <class 'django.db.models.query.ValuesListQuerySet'>

Practically, you have two solutions:

  1. Convert to a python List:
data = list(MyModel.object.all().values_list('id', flat=true))

But again, there is no guarantee that it will work! It depends if the returned value of values_list is iterable or not.

  1. Serialize before passing it to json.dumps:

You can choose what to serialiaze Django has a built-in way to serialize a QuerySet. And if you only want the IDs, you may use the fields kwarg.

1 from django.core import serializers
3 data = serializers.serialize('json', MyModel.objects.all(), fields=('id',))

Hope it helps!