Implementing ListSerializer update for ModelSerializer with HyperlinkedIdentityField

[William Shallum]

Hi,

I am trying to implement an update method for a ListSerializer. The
ListSerializer is for a ModelSerializer which has a
HyperlinkedIdentityField.

The problem I have is since the HyperlinkedIdentityField is read-only,
it does not add to validated_data, so I cannot distinguish between new
objects (without URL) and existing objects (with URL of existing
object). The example in the docs (
http://www.django-rest-framework.org/api-guide/serializers/#customizing-multiple-update
) uses an id attribute that is sent, but I can't get at the
id-equivalent attribute here.

Any tips?

Regards,
William

[Antonis Kalipetis]

Hello William,

I would suggest that the best way would be to use a ListField[1], which you would declare write-only. Then, you'd use this field for getting a list for IDs for the related resources and creating or updating your model, while continue having your HyperlinkedIdentityField for rendering.

For example, changing the example given for HyperlinkedIdentityField[2]:

class AlbumSerializer(serializers.HyperlinkedModelSerializer):
    track_listing = serializers.HyperlinkedIdentityField(view_name='track-list')
    track_list_ids = serializers.ListField(

        child=serializers.IntegerField(min_value=0, max_value=100), write_only=True

    )

    class Meta:
        model = Album
        fields = ('album_name', 'artist', 'track_listing', 'track_list_ids')

Then, you'll be able to update your model using the reference you provided and find the IDs in the new `track_list_ids` field.

ak

[1] http://www.django-rest-framework.org/api-guide/fields/#listfield

[2] http://www.django-rest-framework.org/api-guide/relations/#hyperlinkedidentityfield

[William Shallum]

Hi Antonis,

I have worked around this by creating a write-only field that peeks at the "url" field of the dictionary of data:

class WriteOnlySynonymField(serializers.Field):

    def __init__(self, **kwargs):
        kwargs['default'] = serializers.empty
        kwargs['required'] = False
        kwargs['write_only'] = True
        self.synonym_for = kwargs.pop('synonym_for')
        super(WriteOnlySynonymField, self).__init__(**kwargs)

    def get_value(self, dictionary):
        return dictionary.get(self.synonym_for, serializers.empty)

    def to_internal_value(self, data):
        return data

And it is used as:

submitted_url = WriteOnlySynonymField(synonym_for='url')

Regards,
William

[Antonis Kalipetis]

Great William, that should work too.

ak

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