I have a model named Invitation, where I have created a property method which returns the value returned by __str__() method, like below:

class Invitation(models.Model):
    def __str__(self):
        name = "Sent To: "   self.sent_to   " - Invited To: "   self.invited_to

        if self.accepted_at is not None:
            name = name   " - Accepted On: "   \
                str(self.accepted_at.date())   " (yy-mm-dd) - At: "   str(self.accepted_at.hour)   \
                ":"   str(self.accepted_at.minute)   ":"   str(self.accepted_at.second)   \
                " (hh:mm:ss)"
        
        if self.is_canceled:
            name = name   " - CANCELED"
        elif timezone.now() > self.expiration_date:
            name = name   " - EXPIRED AT: "   str(self.expiration_date)

        return(name)

    @property
    def get_str(self):
        return self.__str__()

Now, I am trying to use this property method in QuerySet's values_list() method as below:

Invitation.objects.values_list("pk", "get_str")

But I am getting following error:

Cannot resolve keyword 'get_str' into field. Choices are: accepted_at, created_at, created_by, created_by_id, expiration_date, id, invited_to, invitee_first_name, invitee_last_name, is_canceled, secret, sent_to

Full Traceback of error is:

Traceback Switch to copy-and-paste view
/app/.heroku/python/lib/python3.10/site-packages/django/db/models/sql/query.py, line 2107, in add_fields
                join_info = self.setup_joins( …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/db/models/sql/query.py, line 1773, in setup_joins
                path, final_field, targets, rest = self.names_to_path( …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/db/models/sql/query.py, line 1677, in names_to_path
                    raise FieldError( …
Local vars
During handling of the above exception (Cannot resolve keyword 'get_str' into field. Choices are: accepted_at, created_at, created_by, created_by_id, expiration_date, id, invited_to, invitee_first_name, invitee_last_name, is_canceled, secret, sent_to), another exception occurred:
/app/.heroku/python/lib/python3.10/site-packages/django/core/handlers/exception.py, line 55, in inner
                response = get_response(request) …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/core/handlers/base.py, line 197, in _get_response
                response = wrapped_callback(request, *callback_args, **callback_kwargs) …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/views/generic/base.py, line 84, in view
            return self.dispatch(request, *args, **kwargs) …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/contrib/auth/mixins.py, line 73, in dispatch
        return super().dispatch(request, *args, **kwargs) …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/views/generic/base.py, line 119, in dispatch
        return handler(request, *args, **kwargs) …
Local vars
/app/apps/accounts/views.py, line 295, in get
        invites = Invitation.objects.get_invites_to_cancel(user) …
Local vars
/app/apps/accounts/models.py, line 551, in get_invites_to_cancel
                values_list("pk", "get_str") …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/db/models/query.py, line 980, in values_list
        clone = self._values(*_fields, **expressions) …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/db/models/query.py, line 943, in _values
        clone.query.set_values(fields) …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/db/models/sql/query.py, line 2425, in set_values
        self.add_fields(field_names, True) …
Local vars
/app/.heroku/python/lib/python3.10/site-packages/django/db/models/sql/query.py, line 2140, in add_fields
                raise FieldError( …
Local vars

What wrong am I doing? What is the proper way to use property method? Any help would be appreciated.

CodePudding user response：

You can annotate field to your qs containing all required fields and then call values_list on that field

qs = Invitation.objects.annotate(
            str=Concat(F('name'), Value(' - '), F('id'), output_field=models.CharField())
        ).values_list('pk', 'str')

result is:

(14, 'zeta - 14')