I'm having a problem creating (nested) serializers for the following models:
class Chapter(Model):
uuid = UUIDField(primary_key=True, editable=False)
description = TextField(blank=True)
class Section(Model):
uuid = UUIDField(primary_key=True, editable=False)
description = TextField(blank=True)
chapter = ForeignKey(Chapter, related_name='sections', on_delete=CASCADE)
Here is the serializer for the Chapter model with the create method:
class ChapterSerializer(ModelSerializer):
uuid = UUIDField(read_only=False)
sections = SectionSerializer(many=True, read_only=False)
class Meta:
model = Chapter
fields = ('uuid', 'description', 'sections')
def create(self, validated_data):
sections = validated_data.pop('sections', [])
chapter = Chapter.objects.create(**validated_data)
for section in sections:
section.update({'chapter': chapter})
section = Section.objects.create(**section)
return chapter
And here are two slightly different variants of the Section serializer:
class SectionSerializer(ModelSerializer):
uuid = UUIDField(read_only=False)
chapter = PrimaryKeyRelatedField(read_only=true)
class Meta:
model = Section
fields = ('uuid', 'description', 'chapter')
class SectionSerializer(ModelSerializer):
uuid = UUIDField(read_only=False)
chapter = PrimaryKeyRelatedField(queryset=Chapter.objects.all())
class Meta:
model = Section
fields = ('uuid', 'description', 'chapter')
Now if I try to create a new Chapter with nested Sections and the
PrimaryKeyRelatedField in the Section serializer has the queryset parameter
set, I get the following error:
'sections': [{'chapter': ['Invalid pk "x" - object does not exist.']}]
I think this error is created while converting the pk to an internal value
<https://github.com/encode/django-rest-framework/blob/master/rest_framework/relations.py#L250>
but
actually sounds more like a validation error ...
If I use the variant with the read_only=true parameter, creating a new
Chapter with nested Sections works, but now I can no longer create a new
Section (Chapter field is set to an existing Chapter UUID) because the
chapter field is removed while validating the input data.
django.db.utils.IntegrityError: null value in column "chapter_id" violates
not-null constraint
I think I could solve this by duplicating the SectionSerializer, but this
seems to be a very crude solution ...
Overall my experience implementing Nested Serializers with DRF is very
frustrating! I think one major problem is, that there are very limited
documentation on this topic! Especially the validation steps are very
unintuitive, as can be seen in the example above:
- Why is the validation step not skipped if I overwrite the validate
methode?
- Why is the pk checked while converting to an internal value?
- Why are read_only fields obmitted (even within the input data to
self.validate!!!!!) and what can I do about this?
- How is the internal validation api working? There are many
methods like run_validation, run_validators, to_internal_value,
validate, validate_empty_values, validators. How are they working together?
(Any why are they always getting in my way?)
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