old_contents: from leaflet.admin import LeafletGeoAdmin
  from django.contrib import admin
  from import_export import resources
  from import_export.admin import ImportExportModelAdmin
  
  # Register your models here.
  from .models import Author, Book, BookInstance, BookHolding, BookOwning, BookBatch
  
  class BookResource(resources.ModelResource):
      class Meta:
          model = Book
  
  class BookAdmin(ImportExportModelAdmin):
      resource_class = BookResource
  
  class BookCodeResource(resources.ModelResource):
      class Meta:
          model = BookInstance
          exclude = ('id','ownings', 'holdings', 'arrived')
          import_id_fields = ['book_code']
          skip_unchanged = True
  
  class BookCodeAdmin(ImportExportModelAdmin):
      resource_class = BookCodeResource
  
  admin.site.register(Author)
  admin.site.register(Book, BookAdmin)
  admin.site.register(BookInstance, BookCodeAdmin)
  admin.site.register(BookHolding, LeafletGeoAdmin)
  admin.site.register(BookOwning, LeafletGeoAdmin)
  admin.site.register(BookBatch, LeafletGeoAdmin)
  
  
new_contents: from leaflet.admin import LeafletGeoAdmin
  from django.contrib import admin
  from import_export import resources
  from import_export.admin import ImportExportModelAdmin
  
  # Register models
  from .models import Author, Book, BookInstance, BookHolding, BookOwning, BookBatch
  from django.contrib.auth.models import User
  
  class BookResource(resources.ModelResource):
      class Meta:
          model = Book
  
  class BookAdmin(ImportExportModelAdmin):
      resource_class = BookResource
  
  class BookCodeResource(resources.ModelResource):
      class Meta:
          model = BookInstance
          exclude = ('id','ownings', 'holdings', 'arrived')
          import_id_fields = ['book_code']
          skip_unchanged = True
  
  class BookCodeAdmin(ImportExportModelAdmin):
      resource_class = BookCodeResource
  
  class UserResource(resources.ModelResource):
      class Meta:
          model = User
          fields = ('first_name', 'last_name', 'email', 'groups', 'username')
          import_id_fields = ['username']
          skip_unchanged = True
  
  class UserAdmin(ImportExportModelAdmin):
      resource_class = UserResource
      pass
  
  admin.site.register(Author)
  admin.site.register(Book, BookAdmin)
  admin.site.register(BookInstance, BookCodeAdmin)
  admin.site.register(BookHolding, LeafletGeoAdmin)
  admin.site.register(BookOwning, LeafletGeoAdmin)
  admin.site.register(BookBatch, LeafletGeoAdmin)
  
  admin.site.unregister(User)
  admin.site.register(User, UserAdmin)
subject: Add option to bulk-add users