example.py

class ContentField(models.ForeignKey):    
    
    def __init__(self, *args, **kwargs):
        self.encodings = kwargs.pop('encodings')
        self.required_fields = set(kwargs.pop('required_fields'))
        args = list(args)
        args.insert(0, 'basecontent.BaseContent')
        super(ContentField, self).__init__(*args,**kwargs)


class ExtendedContent(models.Model):
    """
    Base model for collections of content to be used in building compiled 
    content.
    """
    slug = models.SlugField(max_length=200, unique=True, db_index=True)
    metadata = JSONField()
    
    def __init__(self, *args, **kwargs):
        super(ExtendedContent, self).__init__(*args, **kwargs)
              
    def render(self, context):
        raise NotImplemented("Not Implemented for %s" % self.__name__)

    def compile_src(self):
        dictionary = {}
        for field in self._meta.fields:
            value = getattr(self, field.name)
            if issubclass(field, fields.ContentField):
                item = {
                    'metadata': value.metadata, 
                    'content': value.content,
                }
            elif :
                item = value
                
        return dictionary

class Article(ExtendedContent):
    """
    Test model for Articles.
    """
    body = fields.ContentField(encodings=['md','html'], 
                    required_fields=['title','description'])
    publish_date = models.DateTimeField()