class ReadOnlyManyToManyTests(TestCase):
    def setUp(self):
        class ReadOnlyManyToManySerializer(serializers.ModelSerializer):
            rel = serializers.RelatedField(many=True, read_only=True)

            class Meta:
                model = ReadOnlyManyToManyModel

        self.serializer_class = ReadOnlyManyToManySerializer

        # An anchor instance to use for the relationship
        self.anchor = Anchor()
        self.anchor.save()

        # A model instance with a many to many relationship to the anchor
        self.instance = ReadOnlyManyToManyModel()
        self.instance.save()
        self.instance.rel.add(self.anchor)

        # A serialized representation of the model instance
        self.data = {'rel': [self.anchor.id], 'id': 1, 'text': 'anchor'}

    def test_update(self):
        """
        Attempt to update an instance of a model with a ManyToMany
        relationship.  Not updated due to read_only=True
        """
        new_anchor = Anchor()
        new_anchor.save()
        data = {'rel': [self.anchor.id, new_anchor.id]}
        serializer = self.serializer_class(self.instance, data=data)
        self.assertEqual(serializer.is_valid(), True)
        instance = serializer.save()
        self.assertEqual(len(ReadOnlyManyToManyModel.objects.all()), 1)
        self.assertEqual(instance.pk, 1)
        # rel is still as original (1 entry)
        self.assertEqual(list(instance.rel.all()), [self.anchor])

    def test_update_without_relationship(self):
        """
        Attempt to update an instance of a model where many to ManyToMany
        relationship is not supplied.  Not updated due to read_only=True
        """
        new_anchor = Anchor()
        new_anchor.save()
        data = {}
        serializer = self.serializer_class(self.instance, data=data)
        self.assertEqual(serializer.is_valid(), True)
        instance = serializer.save()
        self.assertEqual(len(ReadOnlyManyToManyModel.objects.all()), 1)
        self.assertEqual(instance.pk, 1)
        # rel is still as original (1 entry)
        self.assertEqual(list(instance.rel.all()), [self.anchor])

    def setUp(self):
        class ReadOnlyManyToManySerializer(serializers.ModelSerializer):
            rel = serializers.RelatedField(many=True, read_only=True)

            class Meta:
                model = ReadOnlyManyToManyModel

        self.serializer_class = ReadOnlyManyToManySerializer

        # An anchor instance to use for the relationship
        self.anchor = Anchor()
        self.anchor.save()

        # A model instance with a many to many relationship to the anchor
        self.instance = ReadOnlyManyToManyModel()
        self.instance.save()
        self.instance.rel.add(self.anchor)

        # A serialized representation of the model instance
        self.data = {'rel': [self.anchor.id], 'id': 1, 'text': 'anchor'}