class Section(models.Model):
    id = models.AutoField(primary_key=True)
    parent = models.ForeignKey('self', default=None,blank=True, null=True)
    name = models.CharField(max_length=100, unique=True)
    visible = models.BooleanField(db_index = True,default=True) 
class Blog(models.Model):
    id = models.AutoField(primary_key=True)
    section_id = models.ForeignKey(Section, default=None,blank=True, null=True)
    description = models.TextField(blank=True)
    created = models.DateTimeField(auto_now_add=True)

from myproject.blog.models import Blog,Section
from django.contrib import admin
admin.site.register(Blog)
admin.site.register(Section)