How do you make a Django Rest Framework serializer bi-directional

Question

I have an angular app that presents a form with contact data and a list of contact numbers. Each contact can have N numbers and each of those numbers has a type (cell,home,work...) The code below will send the json to the angular app just fine and I can deal with it there including adding new numbers, removing numbers ..... However when DRF gets the exact same format json back, it can't deserialize it. It throws off this error:

AttributeError: 'Contact' object has no attribute 'numbers'

which is totally valid, but the serializer DOES have that field and should be able to hang onto those values so I can save them after I save the contact.

If I do something totally hokey like this in the update method:

self.object = self.get_object_or_none()
self.object.numbers = []

I can eliminate that error, but then it throws off these kind of errors:

{'numbers': [
    {u'non_field_errors': [u'Cannot create a new item, only existing items may be updated.']}, 
    {u'non_field_errors': [u'Cannot create a new item, only existing items may be updated.']}, 
    {u'non_field_errors': [u'Cannot create a new item, only existing items may be updated.']}
]}

The first two phone numbers aren't new, they have id fields and came from the db, the third one is new, I'm trying to add it.

Here is the code. Surely this isn't that bizarre a way to do things. Is Django Rest Framework what I should be using? I keep running into show stoppers like this that seem to be the documented way to do things, but then they blow up spectacularly.

class PhoneTypeSerializer(serializers.ModelSerializer):
    class Meta:
        model = PhoneType

class ContactPhoneSerializer(serializers.ModelSerializer):
    number_type = PhoneTypeSerializer(source='number_type')
    class Meta:
        model = ContactPhone
        depth = 1
        exclude = ('owner',)

class ContactSerializer(serializers.ModelSerializer):
    numbers = ContactPhoneSerializer(source='number_set', many=True, required=False)
class Meta:
    model = Contact

How do I deserialize this data so I can save it?

Answer 1

I had the same issue and solved it by adding to the serializer some flags. In your case it should be something like:

number_type = PhoneTypeSerializer(source='number_type',  many=True, required=False, allow_add_remove=True, read_only=False)

A bit late, but maybe it still helps. Found this suggestion here: Updating m2m not possible when using serializers as fields