I ended up creating a custom base class for serializers with a custom
update method like the one you describe. It supports an additional
'immutable_fields' property on the Meta class:
from rest_framework.serializers import ModelSerializer
class BaseSerializer(ModelSerializer):
def update(self, instance, validated_data):
# Get the immutable fields from the Meta class
immutable = getattr(self.Meta, 'immutable_fields', [])
# Save all current values for immutable fields, to restore later
savedValues = {}
for field in immutable:
savedValues[field] = getattr(instance, field, None)
# Call the update method of the parent class to update all fields
obj = super().update(instance, validated_data)
# Restore immutable fields and save object
for field in savedValues:
if savedValues[field] is not None:
setattr(obj, field, savedValues[field])
obj.save()
return obj
On Thursday, October 27, 2016 at 4:45:20 PM UTC+2, Ed B wrote:
>
> I totally agree and I visited this group hoping to find and answer to this
> exact issue. Surely this is a fairly common use-case? In my case I want to
> be able to create a user with a username which should never be changed once
> created.
>
> On Thursday, October 6, 2016 at 4:53:52 PM UTC+2, Mikkel Mortensen wrote:
>>
>> I've several times found myself in the situation of writing separate
>> serializers for creating objects. it's in cases where I have a field that
>> is not quite `read_only`, not quite `write_only`. A better definition would
>> be `create_only`.
>>
>> An example (which is a bit lame) could be when i create a new `Person`.
>> The `PersonSerializer` has `read_only` fields `mother` and `father`, which
>> are other `Person`s that are serialized.
>>
>> What I usually do is to have `mother_id` and `father_id` fields as well,
>> which are `write_only`, to avoid having to supply the complex data
>> structures for whole `Person`s instead of just the `id`.
>>
>> But I don't want to be able to change those after creation, as it's
>> doesn't make (biological) sense to change parents once you're born. I could
>> check that these don't change in the `update` method of the
>> `PersonSerializer`, but that's tedious work.
>>
>> so I always end up writing a separate `NewPersonSerializer` with the
>> `mother_id` and `father_id` fields, which is used for creating new
>> `Person`s.
>>
>> So what i'm sort of missing is a `create_only` field -- a writable field
>> that is only available for creating objects. Has that ever been discussed?
>> Would it make sense to implement? Or is there a better way to achieve what
>> i'm trying to do in a single serializer, other than doing the previously
>> mentioned check in `update`?
>>
>
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