Django REST Framework serializer field required=false

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?

score 56 · Accepted Answer · answered Nov 05 '13 at 08:09

56

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']

answered Nov 05 '13 at 08:09

Kevin Stone

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Hmmm I see, based on your answer, I tried adding validators=[] to serializer fields and still doesn't work. This kind of things are not working as advertised... – James Lin Nov 05 '13 at 18:28
Did you add the `get_validation_exclusions()` method? It overrides the existing validations on the model. – Kevin Stone Nov 05 '13 at 22:09
Yes after adding that method works. I was trying to add validators=[] to avoid overwriting get_validation_exclusions() but it didn't work – James Lin Nov 05 '13 at 22:48
If you read through the source, `ModelSerializer`'s implementation grabs all listed serializer fields that are listed in the serializer, but adds back any model fields that aren't read-only or another ModelSerializer. So, you have to help it out by removing the fields your view code is going to contribute. – Kevin Stone Nov 05 '13 at 23:32
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Thanks, I still think this is a defect/imperfection as per documentation. – James Lin Nov 06 '13 at 06:02
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Tend to agree, you should leave an issue on the project https://github.com/tomchristie/django-rest-framework/issues?state=open – Kevin Stone Nov 06 '13 at 07:39
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I have raised an issue with the author and it's accepted. https://github.com/tomchristie/django-rest-framework/issues/1257 – James Lin Dec 05 '13 at 20:40
In 2020 it seems we do not need this anymore, however, it turned out that if owner is used with `unique_together` it has to be required. As a workaround, set the default=None in the serializer field constructor: https://github.com/encode/django-rest-framework/issues/4456 – math Jan 06 '20 at 15:03
Is everything in django just wanky and broken, every time I do something intuitive django is there to show me NOPE, you need to do some convoluted googling and changing before you do what you are obviously trying to d. – E.Serra Aug 06 '20 at 16:32
You can find better solution here - https://stackoverflow.com/a/29621808/7681229 – smartworld-dm Nov 09 '20 at 09:40

score 35 · Answer 2 · edited Oct 15 '19 at 14:49

35

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

You use it like this in your case:

    class Meta:
        model = models.FavoriteList
        optional_fields = ['owner', ]

edited Oct 15 '19 at 14:49

Olivier Pons

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answered Oct 24 '16 at 20:19

Pankaj Singhal

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I've edited this to add a sample just in case. You should be "up" 40x to be on top because the answer with `get_validation_exclusions()` is not valid anymore (it was never called and PyCharm said there's no other declaration but mine to be found, so it's not the right solution). – Olivier Pons Oct 15 '19 at 14:51
1

I guess you meant 10x. 40x would be 160 which is 4 times 40. I can't do anything to reach there . Thanks for adding the sample, BTW. – Pankaj Singhal Oct 15 '19 at 18:42

score 32 · Answer 3 · answered Dec 15 '16 at 19:40

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.

Check also if the database has columns with NOT NULL option. — ozw1z5rd, May 23 '17 at 10:51

score 17 · Answer 4 · answered Dec 02 '20 at 11:07

In 2020, for DRF 3.12.x, the approach that I prefer the approach that relies on Serializer's extra_kwargs.

So assuming your

class FavoriteListSerializer(serializers.ModelSerializer):
    owner = serializers.IntegerField(required=False)
    class Meta:
        model = models.FavoriteList
        fields = ["owner"]  # and whatever other fields you want to expose
        extra_kwargs = {"owner": {"required": False, "allow_null": True}}

score 3 · Answer 5 · answered Feb 01 '20 at 11:13

If you have unique_together constraint on one of the fields you are trying to set required=False you need to set validators=[] in serializers Meta like

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

Here is the original answer

score 1 · Answer 6 · answered Sep 19 '20 at 10:35

You can also do this:

class ASerializer(serializers.HyperlinkedModelSerializer): 
    owner = serializers.HiddenField(default=serializers.CurrentUserDefault())

    ...

As referred here: https://www.django-rest-framework.org/api-guide/validators/#advanced-field-defaults There you can also find the case when you also wanna let the view show owner

Django REST Framework serializer field required=false

6 Answers6

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