old_contents: from django.contrib import admin
  
  # Register your models here.
  
new_contents: from django.contrib import admin
  from reversion.admin import VersionAdmin
  
  from invoice import models
  
  
  class ProductCategoryAdmin(VersionAdmin):
      pass
  
  
  class ProductSalesAdmin(VersionAdmin):
      pass
  
  
  class QuotationLineAdmin(VersionAdmin):
      pass
  
  
  class QuotationAdmin(VersionAdmin):
      pass
  
  
  class SaleLineAdmin(VersionAdmin):
      pass
  
  
  class SaleAdmin(VersionAdmin):
      pass
  
  
  admin.site.register(models.ProductCategory, ProductCategoryAdmin)
  admin.site.register(models.ProductSales, ProductSalesAdmin)
  admin.site.register(models.QuotationLine, QuotationLineAdmin)
  admin.site.register(models.Quotation, QuotationAdmin)
  admin.site.register(models.SaleLine, SaleLineAdmin)
  admin.site.register(models.Sale, SaleAdmin)
  
subject: ADD initial sales/admin.py