ModelSerializer fields don't obey default from the model #4703
Description
Currently, in django, even if a field doesn't have an explicit default=None, the implicit default is going to be None (technically, it's django.db.models.fields.NOT_PROVIDED). However, even if an explicit default is set on a field on the model, the serializer will ignore it.
This comes up in the context of PUT/PATCH, where one will (I know I did) expect PUT to put the default value for fields not passed that, at the very least, have an explicit default.
To give an example, a model with a field that is:
foo = models.PositiveSmallIntegerField(null=True, blank=True, default=42)
will generate the following field in the serializer:
foo = IntegerField(allow_null=True, max_value=32767, min_value=0, required=False)
The default value will be used when creating the instance, but not on PUT updates.
So, two things need to be discussed/decided:
- Should fields that have an explicit default move that on to the serializer so that a PUT will populate the default value? - I would say a definite yes here, the current behaviour is surprising and undocumented (Or, I couldn't find it in the docs)
- Should fields with implicit default (django.db.models.fields.NOT_PROVIDED) behave similarly and null out fields not provided for a PUT? - I would say no here, this is too big a change in behaviour and also might be surprising to other people.