How to filter with a non non-model field?

I have a model with one of its fields is a random generated string as the following

from django.utils.crypto import get_random_string
class Competition(models.Model):
    name = models.CharField(verbose_name="challenge name", max_length=256)
    start_date = models.DateTimeField(verbose_name="start date")
    end_date = models.DateTimeField(verbose_name="end date")
    code = get_random_string(length=6)
    owner = models.ForeignKey(User, related_name="owner", on_delete=models.CASCADE)
    def __str__(self):
        return self.name

I am trying to have an endpoint like thathttp://192.168.1.2:8000/competitions/?code=${some_string} to access from react frontend. so in order to do so I have some filters

from django_filters import rest_framework as filters

class CompetitionFilter(filters.FilterSet):
    class Meta:
        model = competition
        fields = {
            "name": ["exact", "icontains"],
            "code": ["exact"],
            "start_date": ["exact", "lte", "gte"],
            "end_date": ["exact", "lte", "gte"],
            "owner": ["exact"],
        }

but I have an error saying TypeError: 'Meta.fields' must not contain non-model field names: code So how can I achieve it?