Improve checks for nested creates and updates.

[tomchristie]

Closes #2194.

[kevin-brown]

LGTM, same fix I was planning on making. 👍

[baylee]

@tomchristie @kevin-brown thanks for the 3.0.1 release. I just updated and my tests are failing with this new addition (The .create() method does not support writable nestedfields by default.), but as far as I know I'm not attempting to do any nested writes. I have one related Serializer, but it is set to read_only=True and when I post to this endpoint, the related objects all already exist. Any ideas, or am I just doing something wrong?

class Like(models.Model):
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField(db_index=True)
    content_object = generic.GenericForeignKey()

    user = models.ForeignKey(settings.AUTH_USER_MODEL)

    class Meta:
        unique_together = (("user", "content_type", "object_id"),)


class LikeSerializer(serializers.ModelSerializer):
    user = UserSerializer(read_only=True, default=serializers.CurrentUserDefault())

    class Meta:
        model = Like


class LikeViewSet(viewsets.ModelViewSet):
    queryset = Like.objects.all()
    serializer_class = LikeSerializer

    def perform_create(self, serializer):
        serializer.save(user=self.request.user)

    def perform_update(self, serializer):
        serializer.save(user=self.request.user)

printed LikeSerializer

LikeSerializer():
    id = IntegerField(label='ID', read_only=True)
    user = UserSerializer(default=CurrentUserDefault(), read_only=True):
        email = EmailField(allow_blank=True, allow_null=True, max_length=75, required=False, validators=[<UniqueValidator(queryset=User.objects.all())>])
        id = IntegerField(label='ID', read_only=True)
        username = CharField(help_text='Required. 30 characters or fewer. Letters, digits and @/./+/-/_ only.', max_length=30, validators=[<django.core.validators.RegexValidator object>, <UniqueValidator(queryset=User.objects.all())>])
        fullname = CharField(allow_blank=True, allow_null=True, max_length=80, required=False)
        original_photo = ImageField(allow_null=True, max_length=100, required=False)
        about = CharField(allow_blank=True, allow_null=True, required=False, style={'type': 'textarea'})
        user_following_count = ReadOnlyField()
        user_followers_count = ReadOnlyField()
        content_type = SerializerMethodField()
    created = DateTimeField(read_only=True)
    object_id = IntegerField(required=True)
    content_type = PrimaryKeyRelatedField(queryset=ContentType.objects.all(), required=True)
    class Meta:
        validators = [<UniqueTogetherValidator(queryset=Like.objects.all(), fields=('user', 'content_type', 'object_id'))>]

I'm just posting the object_id and content_type of the object I want to like. Was working fine before I updated.

Thanks!

[xordoquy]

@baylee the support questions are better asked on the mailing list or stack overflow.

[baylee]

Okay, here it is on SO: http://stackoverflow.com/questions/27452044/drf-3-0-1-create-method-does-not-support-writable-nestedfields

Any explanation or corrections would be appreciated.

[tomchristie]

This does actually highlight a possible improvement we could make to that check.

As both 'read_only' and 'default' are being using this isn't actually a nested write, although it does fail our test.