fix: Add support for unique_together to UniqueFieldsMixin

drf_writable_nested/mixins.py

@@ -10,7 +10,7 @@
 from django.utils.translation import gettext_lazy as _
 from rest_framework import serializers
 from rest_framework.exceptions import ValidationError
-from rest_framework.validators import UniqueValidator
+from rest_framework.validators import UniqueTogetherValidator, UniqueValidator
 
 
 class BaseNestedModelSerializer(serializers.ModelSerializer):
@@ -400,12 +400,14 @@ class Meta:
     (`UniqueFieldsMixin` and `NestedCreateMixin` or `NestedUpdateMixin`)
     you should put `UniqueFieldsMixin` ahead.
     """
-    _unique_fields = []  # type: List[Tuple[str,UniqueValidator]]
+    _unique_fields = []  # type: List[Tuple[str, UniqueValidator]]
+    _unique_together_validators = []  # type: List[UniqueTogetherValidator]
 
     def get_fields(self):
         self._unique_fields = []
 
         fields = super(UniqueFieldsMixin, self).get_fields()
+
         for field_name, field in fields.items():
             unique_validators = [validator
                                  for validator in field.validators
@@ -419,6 +421,10 @@ def get_fields(self):
 
         return fields
 
+    def get_unique_together_validators(self):
+        self._unique_together_validators = super().get_unique_together_validators()
+        return []
+
     def _validate_unique_fields(self, validated_data):
         for unique_field in self._unique_fields:
             field_name, unique_validator = unique_field
@@ -434,6 +440,8 @@ def _validate_unique_fields(self, validated_data):
                                      self.fields[field_name])
             except ValidationError as exc:
                 raise ValidationError({field_name: exc.detail})
+        for validator in self._unique_together_validators:
+            validator(validated_data, self)
 
     def create(self, validated_data):
         self._validate_unique_fields(validated_data)

tests/migrations/0003_add_itemcategory_and_more.py

@@ -0,0 +1,32 @@
+# Generated by Django 5.2.6 on 2025-09-14 14:12
+
+import django.db.models.deletion
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('tests', '0002_alter_profile_sites_setnullforeignkey_and_more'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='ItemCategory',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('name', models.CharField(max_length=50)),
+                ('company', models.CharField(max_length=50)),
+            ],
+            options={
+                'unique_together': {('name', 'company')},
+            },
+        ),
+        migrations.CreateModel(
+            name='ItemParent',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('child', models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='tests.itemcategory')),
+            ],
+        ),
+    ]

tests/models.py

@@ -128,6 +128,20 @@ class UFMParent(models.Model):
     child = models.ForeignKey(UFMChild, on_delete=models.CASCADE)
 
 
+class ItemCategory(models.Model):
+    name = models.CharField(max_length=50)
+    company = models.CharField(max_length=50)
+
+    class Meta:
+        unique_together = (
+            ("name", "company"),
+        )
+
+
+class ItemParent(models.Model):
+    child = models.ForeignKey(ItemCategory, on_delete=models.CASCADE)
+
+
 # Models for different relations
 
 class ForeignKeyChild(models.Model):

tests/serializers.py

@@ -228,6 +228,20 @@ class Meta:
         model = models.UFMParent
         fields = ('pk', 'child')
 
+# UniqueFieldsMixin, unique_together validation serializers
+
+class ItemCategorySerializer(UniqueFieldsMixin, serializers.ModelSerializer):
+    class Meta:
+        model = models.ItemCategory
+        fields = "__all__"
+
+
+class ItemParentSerializer(WritableNestedModelSerializer):
+    child = ItemCategorySerializer()
+
+    class Meta:
+        model = models.ItemParent
+        fields = "__all__"
 
 # Different relations
 

tests/test_unique_fields_mixin.py

@@ -101,3 +101,65 @@ def test_unique_field_not_required_for_partial_updates(self):
         )
         self.assertTrue(serializer.is_valid())
         serializer.save()
+
+
+class UniqueFieldsMixinUniqueTogetherTestCase(TestCase):
+    def test_create_update_success(self):
+        serializer = serializers.ItemParentSerializer(
+            data={'child': {'name': 'Video Cards', 'company': 'Example'}})
+        self.assertTrue(serializer.is_valid())
+        parent = serializer.save()  # type: models.ItemParent
+
+        serializer = serializers.ItemParentSerializer(
+            instance=parent,
+            data={
+                'pk': parent.pk,
+                'child': {
+                    'pk': parent.child.pk,
+                    'name': 'value',
+                    'company': 'value',
+                }
+            }
+        )
+        self.assertTrue(serializer.is_valid())
+        serializer.save()
+
+    def test_create_update_failed(self):
+        # In this case everything is valid on the validation stage, because
+        # UniqueTogetherValidator is skipped
+        # But `save` should raise an exception on create/update
+
+        child = models.ItemCategory.objects.create(name='value', company='value')
+        parent = models.ItemParent.objects.create(child=child)
+
+        default_error_detail = ErrorDetail(
+            string='The fields name, company must make a unique set.',
+            code='unique')
+        serializer = serializers.ItemParentSerializer(
+            data={
+                'child': {
+                    'name': child.name,
+                    'company': child.company,
+                }
+            }
+        )
+
+        self.assertTrue(serializer.is_valid())
+
+        with self.assertRaises(ValidationError) as ctx:
+            serializer.save()
+        self.assertEqual(
+            ctx.exception.detail,
+            {'child': [default_error_detail]}
+        )
+
+
+    def test_unique_field_not_required_for_partial_updates(self):
+        child = models.ItemCategory.objects.create(name='value', company='value')
+        serializer = serializers.ItemCategorySerializer(
+            instance=child,
+            data={},
+            partial=True
+        )
+        self.assertTrue(serializer.is_valid())
+        serializer.save()