[Django]: Template を models に入れる

from django.db import models
from django.contrib.sites.models import Site
from datetime import datetime


class Block(models.Model):
    name = models.CharField(blank=False, maxlength=200)
    slug = models.SlugField(blank=False, maxlength=20, unique=True)
    url = models.URLField(blank=False, verify_exists=False,\
                            default="http://%s/#slug" % Site.objects.get_current(), )
    default_template = models.TextField(blank=False, default='<div id="slug"></div>')
    add = models.DateTimeField(auto_now_add=True, editable=False)
    mod = models.DateTimeField(auto_now=True, editable=False)

    def __str__(self):
        return "%s" % self.name

    def get_absolute_url(self):
        return self.url


class Source(models.Model):
    block = models.ForeignKey(Block)
    open_date = models.DateTimeField(blank=False, default=datetime.now())
    enabled = models.BooleanField(default=True)
    template = models.TextField(blank=False)
    add = models.DateTimeField(auto_now_add=True, editable=False)
    mod = models.DateTimeField(auto_now=True, editable=False)

    def __str__(self):
        return "%s" % self.block.name

    def get_absolute_url(self):
        return self.block.url

    class Meta:
        get_latest_by = "open_date"

from django.template import Node, Library, Context, Template, TemplateSyntaxError
from myproject.app.models import Block, Source
from datetime import datetime

register = Library()

class TemplateRender(Node):
    def __init__(self, name):
        try:
            self.template = Source.objects.filter(
                        block__slug=name, enabled=True, open_date__lte=datetime.now()
                        ).latest().template
        except Source.DoesNotExist:
            try:
                self.template = Block.objects.get(slug=name).default_template
            except Block.DoesNotExist:
                self.template = None

    def render(self, context):
        if self.template:
            self.t = Template(self.template)
            return self.t.render(context)
        else:
            return ""

def template_render(parser, token):
    tag_name, strings = token.split_contents()
    bits = strings.split()
    if not len(bits) == 1:
        raise TemplateSyntaxError
    return TemplateRender(bits[0])

register.tag(template_render)

>>> from django.template import Context, Template
>>> t = Template("{% load app_extras %}{% template_render slug %}")
>>> t.render(Context({}))
'<div id="slug"></div>'