from django.db import models
class OtherExample(models.Model):
 pass
class Example(models.Model):
 other_example = models.ForeignKey(
 to=OtherExample,
 on_delete=models.CASCADE,
 )
 class Meta:
 constraints = [
 models.UniqueConstraint(
 fields=[
 "id",
 # "other_example_id", # this questionably raises AssertionError: May not set both `read_only` and `required`
 "other_example", # this does not raise, but probably should raise something
 ],
 name="unique_id_and_other_example",
 )
 ]
from rest_framework import serializers
class ExampleModelSerializer(serializers.ModelSerializer):
 # other_example_id = serializers.IntegerField() # another workaround
 class Meta:
 model = Example
 fields = [
 "id",
 "other_example_id",
 ]
from django.test import TestCase
class TestExampleModelSerializer(TestCase):
 def test_unique_constraint(self):
 ser = ExampleModelSerializer(data={"id": 1, "other_example_id": 1})
 assert ser.is_valid()