Exclude read_only=True fields from unique_together validation

rest_framework/serializers.py

@@ -1243,6 +1243,11 @@ class ModelSerializer(Serializer):
 
         read_only_fields = getattr(self.Meta, 'read_only_fields', None)
         if read_only_fields is not None:
+            if not isinstance(read_only_fields, (list, tuple)):
+                raise TypeError(
+                    'The `read_only_fields` option must be a list or tuple. '
+                    'Got %s.' % type(read_only_fields).__name__
+                )
             for field_name in read_only_fields:
                 kwargs = extra_kwargs.get(field_name, {})
                 kwargs['read_only'] = True
@@ -1390,6 +1395,7 @@ class ModelSerializer(Serializer):
         field_names = {
             field.source for field in self.fields.values()
             if (field.source != '*') and ('.' not in field.source)
+            and not field.read_only
         }
 
         # Note that we make sure to check `unique_together` both on the

tests/test_model_serializer.py

@@ -521,8 +521,6 @@ class TestRelationalFieldMappings(TestCase):
                 one_to_one = NestedSerializer(read_only=True):
                     url = HyperlinkedIdentityField(view_name='onetoonetargetmodel-detail')
                     name = CharField(max_length=100)
-                class Meta:
-                    validators = [<UniqueTogetherValidator(queryset=UniqueTogetherModel.objects.all(), fields=('foreign_key', 'one_to_one'))>]
         """)
         if six.PY2:
             # This case is also too awkward to resolve fully across both py2

tests/test_validators.py

@@ -239,6 +239,26 @@ class TestUniquenessTogetherValidation(TestCase):
         """)
         assert repr(serializer) == expected
 
+    def test_ignore_read_only_fields(self):
+        """
+        When serializer fields are read only, then uniqueness
+        validators should not be added for that field.
+        """
+        class ReadOnlyFieldSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = UniquenessTogetherModel
+                fields = ('id', 'race_name', 'position')
+                read_only_fields = ('race_name',)
+
+        serializer = ReadOnlyFieldSerializer()
+        expected = dedent("""
+            ReadOnlyFieldSerializer():
+                id = IntegerField(label='ID', read_only=True)
+                race_name = CharField(read_only=True)
+                position = IntegerField(required=True)
+        """)
+        assert repr(serializer) == expected
+
     def test_ignore_validation_for_null_fields(self):
         # None values that are on fields which are part of the uniqueness
         # constraint cause the instance to ignore uniqueness validation.