Django Rest Framework: How to set a field to null via PATCH request?

Question

I have a Model and a ModelSerializer with this field:

models.py:

leftovers_from = models.ForeignKey('DayPlanning', null=True, blank=True, related_name='extra_for', on_delete=models.CASCADE)

serializers.py:

leftovers_from_id = serializers.PrimaryKeyRelatedField(queryset=DayPlanning.objects.all(), source='leftovers_from', write_only=True, required=False)

Now I can perfectly fine create a new object for this model using a POST request (both with or without this field being null/None/empty.)

However when I try to update the field using PATCH I can only update it with a different value (a PK of the Foreign model). I've tried passing null, '', 0 and -1 to leftovers_from_id, however the result is either This field cannot be empty or PK 0 not found.

How do I clear this field using a PATCH request?

Thanks!

Answer 1

Note that required means the field may be omitted for creation or "full" update. Patch bypasses the required fields to achieve a partial update.

Therefore you'll need to set allow_null argument to True:

leftovers_from_id = serializers.PrimaryKeyRelatedField(
    queryset=DayPlanning.objects.all(),
    source='leftovers_from', write_only=True,
    required=False, allow_null=True,
)

Then you should be able to PATCH with:

{'leftovers_from_id': null}

Answer 2

To clear the relation, you should set the value to None. Since you specifically mentioned PATCH methods, make sure you're aware of the partial argument as well: http://www.django-rest-framework.org/api-guide/serializers/#partial-updates