django rest framework and model inheritance

Question

I have an "abstract" model class MyField:

class MyField(models.Model):
    name = models.CharField(db_index = True, max_length=100)
    user = models.ForeignKey("AppUser", null=False)

I have a few other subclasses of MyField each defining a value of a specific type. for example:

class MyBooleanField(MyField):
    value = models.BooleanField(db_index = True, default=False)

In MyField I have a method get_value() that returns the value based on the specific subclass.

In django rest I want to fetch all the fields of a user

class AppUserSerializer(serializers.ModelSerializer):
    appuserfield_set = MyFieldSerializer(many=True)
    class Meta:
        model = AppUser
        fields = ('appuser_id', 'appuserfield_set')

On the client side I want the user to be able to add new fields and set values to them and then on the server I want to be able to create the correct field based on the value.

What is the correct way to achieve this behavior?

elewinso · Accepted Answer · 2014-04-16 18:15:35Z

After some digging, here is what I ended up doing. Aside from the code below I had to implement get_or_create and create the relevant subclass of MyField based on the passed value.

class ValueField(serializers.WritableField):
  #called when serializing a field to a string. (for example when calling seralizer.data)
  def to_native(self, obj):
    return obj;

  """
  Called when deserializing a field from a string
  (for example when calling is_valid which calles restore_object)
  """
  def from_native(self, data):
    return data


class MyFieldSerializer(serializers.ModelSerializer):
  value = ValueField(source='get_value', required=False)    

  def restore_object(self, attrs, instance=None):
    """
    Called by is_valid (before calling save)
    Create or update a new instance, given a dictionary
    of deserialized field values.

    Note that if we don't define this method, then deserializing
    data will simply return a dictionary of items.
    """
    if instance:
        # Update existing instance
        instance.user = attrs.get('user', instance.user)
        instance.name = attrs.get('name', instance.name)
    else:
        # Create new instance
        instance = MyField.get_or_create(end_user=attrs['user'],
                                            name=attrs['name'],
                                            value=attrs['get_value'])[0]

    instance.value = attrs['get_value']
    return instance

  def save_object(self, obj, **kwargs):
    #called when saving the instance to the DB
    instance = MyField.get_or_create(end_user=obj.user,
                                            name=obj.name,
                                            value=obj.value)[0]
  class Meta:
    model = MyField
    fields = ('id', 'user', 'name', 'value')

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