old_contents: from django.contrib import admin
  from django.conf.urls.defaults import patterns
  from invoice.models import Invoice, InvoiceItem
  from invoice.views import pdf_view
  from invoice.forms import InvoiceAdminForm
  
  
  class InvoiceItemInline(admin.TabularInline):
      model = InvoiceItem
  
  
  class InvoiceAdmin(admin.ModelAdmin):
      inlines = [InvoiceItemInline,]
      fieldsets = (
          (None, {
              'fields': ('user', 'address', 'status')
          }),
          ('Dates', {
              'fields': ('invoice_date', 'due_date', 'paid_date')
          }),
      )
      search_fields = ('invoice_id', 'user__username')
      list_filter = ('status',)
      list_display = (
          'invoice_id',
          'user',
          'invoice_date',
          'due_date',
          'status',
          'total_amount',
      )
      form = InvoiceAdminForm
  
      def get_urls(self):
          urls = super(InvoiceAdmin, self).get_urls()
          return patterns('',
              (r'^(.+)/pdf/$', self.admin_site.admin_view(pdf_view))
          ) + urls
  
  
  admin.site.register(Invoice, InvoiceAdmin)
new_contents: from django.contrib import admin
  from django.conf.urls.defaults import patterns
  from invoice.models import Invoice, InvoiceItem
  from invoice.views import pdf_view
  from invoice.forms import InvoiceAdminForm
  
  
  class InvoiceItemInline(admin.TabularInline):
      model = InvoiceItem
  
  
  class InvoiceAdmin(admin.ModelAdmin):
      inlines = [InvoiceItemInline,]
      fieldsets = (
          (None, {
              'fields': ('user', 'address', 'status')
          }),
          ('Dates', {
              'fields': ('invoice_date', 'due_date', 'paid_date')
          }),
      )
      search_fields = ('invoice_id', 'user__username')
      list_filter = ('status',)
      list_display = (
          'invoice_id',
          'user',
          'invoice_date',
          'due_date',
          'paid_date',
          'status',
          'total_amount',
      )
      form = InvoiceAdminForm
  
      def get_urls(self):
          urls = super(InvoiceAdmin, self).get_urls()
          return patterns('',
              (r'^(.+)/pdf/$', self.admin_site.admin_view(pdf_view))
          ) + urls
  
  
  admin.site.register(Invoice, InvoiceAdmin)
  
subject: Add paid_date to invoice list.