old_contents: from django import forms
  from django.contrib import admin
  from django.utils.translation import ugettext_lazy as _
  
  from . import models
  
  
  admin.site.register(models.Producer,
      list_display=('is_active', 'name', 'ordering'),
      list_display_links=('name',),
      prepopulated_fields={'slug': ('name',)},
      search_fields=('name', 'description'),
      )
  
new_contents: from django import forms
  from django.contrib import admin
  from django.utils.translation import ugettext_lazy as _
  
  from . import models
  
  
  admin.site.register(models.Producer,
      list_display=('is_active', 'name', 'ordering'),
      list_display_links=('name',),
      prepopulated_fields={'slug': ('name',)},
      search_fields=('name', 'description'),
      )
  
  product_admin = admin.site._registry.get(models.Product)
  if product_admin:
      product_admin.list_display += ('producer',)
      product_admin.list_filter += ('producer',)
  
subject: Add producers to admin product change list