old_contents: from django.db import models
  
  # Create your models here.
  
new_contents: from django.db import models
  
  class Gear(models.Model):
  	name = models.CharField(max_length=64)
  	purchase_date = models.DateTimeField('date purchased')
  
  class Camera(Gear):
  	chip_size = models.IntegerField()
  
  class Telescope(Gear):
  	focal_length = models.IntegerField()
  	aperture = models.IntegerField()
  
  class Mount(Gear):
  
  class FocalReduced(Gear):
  	ratio = models.DoubleField()
  
  class Subject(models.Model):
  	name = model.CharField(max_length=64)
  
  	# gear
  	camera = models.ForeignKey(Camera)
  	focal_reducer = models.ForegnKey(FocalReducer)
  	telescope = models.ForeignKey(Telescope)
  	mount = models.ForeignKey(Mount)
  
  	# data
  
subject: Add models.