class Post(models.Model):
    title = models.CharField(max_length=200)
    slug = models.CharField(max_length=200)

    source_url = models.URLField()

    needs_update = models.BooleanField(default=True)

    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)


#models.py
class ItemBase(models.Model):
    post = models.ManyToManyField(Post, related_name='%(class)s_related')
    title = models.CharField(max_length=250)
    created = models.DateTimeField(auto_now_add=True)
    updated = models.DateTimeField(auto_now=True)

    class Meta:
        abstract = True

    def __str__(self):
        return self.title

    def render(self):
        return render_to_string('content/items/{}.html'.format(self._meta.model_name), {'item': self})


class Text(ItemBase):
    content = models.TextField()


class File(ItemBase):
    file = models.FileField(upload_to='files', blank=True, null=True)


class Video(ItemBase):
    url = models.URLField()



class Image(ItemBase):
    image_url = models.URLField(blank=True, null=True)
    image_file = models.ImageField(upload_to='posts/%Y/%m/%d',
                                   blank=True, null=True)

#admin.py
from django.contrib import admin
from .models import Post



@admin.register(Post)
class PostAdmin(admin.ModelAdmin):
    list_display = ['title', 'needs_update', 'created']
    list_filter = ['created', 'needs_update']
    fields = ('title', 'image_related')