Django REST Framework serializer field required=fa

Question

from the documentation:

read_only Set this to True to ensure that the field is used when serializing a representation, but is not used when updating an instance during deserialization.

Defaults to False

required Normally an error will be raised if a field is not supplied during deserialization. Set to false if this field is not required to be present during deserialization.

Defaults to True.

So I have a model which has a field that's not nullable but I want it to be populated in the pre_save method, so I have set the field to required=False in serializer, but doesn't seem to work. I am still getting error when saving the record.

class FavoriteListSerializer(serializers.ModelSerializer):
    owner = serializers.IntegerField(required=False)
    class Meta:
        model = models.FavoriteList

Update: I have added serializer_class = serializers.FavoriteListSerializer to the ViewSet, now instead of getting This field is required, which I think got past the validation but then I am getting This field cannot be null. I have checked the pre_save method is not being executed, any ideas?

Answer 1

Yeah, I ran into this issue at some point as well. You need to also update the validation exclusions.

class FavoriteListSerializer(serializers.ModelSerializer):
    owner = serializers.IntegerField(required=False)
    class Meta:
        model = models.FavoriteList

    def get_validation_exclusions(self):
        exclusions = super(FavoriteListSerializer, self).get_validation_exclusions()
        return exclusions + ['owner']

Answer 2

Late Entry to this thread. This issue was fixed in django-rest-framework 2.3.13. Here is the link of the PR.

Answer 3

In case somebody lands here with a similar issue, pay attention to the following attributes along with required:

allow_blank:

If set to True then the empty string should be considered a valid value.

allow_null:

Normally an error will be raised if None is passed to a serializer field.

required:

Normally an error will be raised if a field is not supplied during deserialization.

I was straggling to figure out why I was getting a validation error with required=False where I had missed the allow_null attribute.

Answer 4

I suppose method .get_validation_exclusions() is now removed. I did not found it in ModelSerializer doc and it did not execute after override (djangorestframework==3.8.2). And i am not the only one facing this problem.

My solution is to just add default value for field which i want to be non-required. It supposed to be fine specifically for situations with pre_save:

class FavoriteListSerializer(serializers.ModelSerializer):
    owner = serializers.IntegerField(default='')
    class Meta:
        model = models.FavoriteList

You also have to keep in mind that using drf serializers with pre_save signals may cause implicit behavour (i did not check, but it seems to be logical):

pre_save is called on pre object save (incredible) which (probably) means after serializer validation.