Polymorphic serializer

polymorphicserializer.py

from rest_framework import serializers
from rest_framework.utils.serializer_helpers import BindingDict

class PolymorphicModelSerializer(serializers.ModelSerializer):
    """
    Serializer that serializes a polymorphic model

    Since the whole point of polymorphism is to have models
    with different properties in the same queryset, the ``fields`` meta
    specification in rest_framework becomes rather useless. That is
    why a new meta specification called ``excluded_fields`` is added,
    which should be more useful.
    
    Usage:

    >>> class PolymorphicSomethingSerializer(PolymorphicModelSerializer):
    >>>    class Meta:
    >>>        model = Something # the polymorphic base class
    >>>        excluded_fields = ['polymorphic_ctype']
    """

    def __init__(self, *args, **kwargs):
        super(PolymorphicModelSerializer, self).__init__(*args, **kwargs)
        self.fields_table = {}
        self.original_model = self.Meta.model

    def to_representation(self, data):
        self.Meta.model = type(data) if data else self.original_model
        return super(PolymorphicModelSerializer, self).to_representation(data)

    @serializers.ModelSerializer.fields.getter
    def fields(self):
        _fields = self.fields_table.get(self.Meta.model, None)
        if _fields is None:
            _excluded_fields = getattr(self.Meta, 'excluded_fields')
            _fields = BindingDict(self)
            for key, value in self.get_fields().items():
                if key not in _excluded_fields:
                    _fields[key] = value
            self.fields_table[self.Meta.model] = _fields
        return _fields