Fixed #19414 -- Added admin registration decorator

Thanks stavros for the suggestion.

django/contrib/admin/__init__.py

 # ACTION_CHECKBOX_NAME is unused, but should stay since its import from here
 # has been referenced in documentation.
+from django.contrib.admin.decorators import register
 from django.contrib.admin.helpers import ACTION_CHECKBOX_NAME
 from django.contrib.admin.options import ModelAdmin, HORIZONTAL, VERTICAL
 from django.contrib.admin.options import StackedInline, TabularInline

django/contrib/admin/decorators.py

+def register(*models, **kwargs):
+    """
+    Registers the given model(s) classes and wrapped ModelAdmin class with
+    admin site:
+
+    @register(Author)
+    class AuthorAdmin(admin.ModelAdmin):
+        pass
+
+    A kwarg of `site` can be passed as the admin site, otherwise the default
+    admin site will be used.
+    """
+    from django.contrib.admin import ModelAdmin
+    from django.contrib.admin.sites import site, AdminSite
+
+    def _model_admin_wrapper(admin_class):
+        admin_site = kwargs.pop('site', site)
+
+        if not isinstance(admin_site, AdminSite):
+            raise ValueError('site must subclass AdminSite')
+
+        if not issubclass(admin_class, ModelAdmin):
+            raise ValueError('Wrapped class must sublcass ModelAdmin.')
+
+        admin_site.register(models, admin_class=admin_class)
+
+        return admin_class
+    return _model_admin_wrapper

docs/ref/contrib/admin/index.txt

@@ -101,6 +101,34 @@ Other topics
 
             admin.site.register(Author)
 
+The register decorator
+----------------------
+
+.. function:: register(*models, [site=django.admin.sites.site])
+
+    .. versionadded:: 1.7
+
+    There is also a decorator for registering your ``ModelAdmin`` classes::
+
+        from django.contrib import admin
+        from .models import Author
+
+        @admin.register(Author)
+        class AuthorAdmin(admin.ModelAdmin):
+            pass
+
+    It is given one or more model classes to register with the ``ModelAdmin``
+    and an optional keyword argument ``site`` if you are not using the default
+    ``AdminSite``::
+
+        from django.contrib import admin
+        from .models import Author, Reader, Editor
+        from myproject.admin_site import custom_admin_site
+
+        @admin.register(Author, Reader, Editor, site=custom_admin_site)
+        class PersonAdmin(admin.ModelAdmin):
+            pass
+
 ``ModelAdmin`` options
 ----------------------
 

docs/releases/1.7.txt

@@ -135,6 +135,10 @@ Minor features
   customize the value of :attr:`ModelAdmin.fields
   <django.contrib.admin.ModelAdmin.fields>`.
 
+* In addition to the existing ``admin.site.register`` syntax, you can use the
+  new :func:`~django.contrib.admin.register` decorator to register a
+  :class:`~django.contrib.admin.ModelAdmin`.
+
 :mod:`django.contrib.auth`
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 

tests/admin_registration/models.py

@@ -8,9 +8,15 @@ from django.db import models
 class Person(models.Model):
     name = models.CharField(max_length=200)
 
+
+class Traveler(Person):
+    pass
+
+
 class Location(models.Model):
     class Meta:
         abstract = True
 
+
 class Place(Location):
     name = models.CharField(max_length=200)

tests/admin_registration/tests.py

 from __future__ import unicode_literals
 
 from django.contrib import admin
+from django.contrib.admin.decorators import register
+from django.contrib.admin.sites import site
 from django.core.exceptions import ImproperlyConfigured
 from django.test import TestCase
 
-from .models import Person, Place, Location
+from .models import Person, Place, Location, Traveler
 
 
 class NameAdmin(admin.ModelAdmin):
     list_display = ['name']
     save_on_top = True
 
+
+class CustomSite(admin.AdminSite):
+    pass
+
+
 class TestRegistration(TestCase):
     def setUp(self):
         self.site = admin.AdminSite()
@@ -62,3 +69,55 @@ class TestRegistration(TestCase):
         Refs #12004.
         """
         self.assertRaises(ImproperlyConfigured, self.site.register, Location)
+
+
+class TestRegistrationDecorator(TestCase):
+    """
+    Tests the register decorator in admin.decorators
+
+    For clarity:
+
+        @register(Person)
+        class AuthorAdmin(ModelAdmin):
+            pass
+
+    is functionally equal to (the way it is written in these tests):
+
+        AuthorAdmin = register(Person)(AuthorAdmin)
+    """
+    def setUp(self):
+        self.default_site = site
+        self.custom_site = CustomSite()
+
+    def test_basic_registration(self):
+        register(Person)(NameAdmin)
+        self.assertTrue(
+            isinstance(self.default_site._registry[Person],
+                       admin.options.ModelAdmin)
+        )
+
+    def test_custom_site_registration(self):
+        register(Person, site=self.custom_site)(NameAdmin)
+        self.assertTrue(
+            isinstance(self.custom_site._registry[Person],
+                       admin.options.ModelAdmin)
+        )
+
+    def test_multiple_registration(self):
+        register(Traveler, Place)(NameAdmin)
+        self.assertTrue(
+            isinstance(self.default_site._registry[Traveler],
+                       admin.options.ModelAdmin)
+        )
+        self.assertTrue(
+            isinstance(self.default_site._registry[Place],
+                       admin.options.ModelAdmin)
+        )
+
+    def test_wrapped_class_not_a_model_admin(self):
+        self.assertRaisesMessage(ValueError, 'Wrapped class must sublcass ModelAdmin.',
+            register(Person), CustomSite)
+
+    def test_custom_site_not_an_admin_site(self):
+        self.assertRaisesMessage(ValueError, 'site must subclass AdminSite',
+            register(Person, site=Traveler), NameAdmin)