[1.0.X] Fixed #8248: made help() work on models and improved introspection support.

Descriptors now return themselves when accessed via the class, as per standard
Python descriptors like property().

Backported from r9550 and also r9562 and r9563


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9634 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/admin/validation.py

@@ -36,6 +36,8 @@ def validate(cls, model):
                         except models.FieldDoesNotExist:
                             raise ImproperlyConfigured("%s.list_display[%d], %r is not a callable or an attribute of %r or found in the model %r."
                                 % (cls.__name__, idx, field, cls.__name__, model._meta.object_name))
+                    else:
+                        # getattr(model, field) could be an X_RelatedObjectsDescriptor
                         f = fetch_attr(cls, model, opts, "list_display[%d]" % idx, field)
                         if isinstance(f, models.ManyToManyField):
                             raise ImproperlyConfigured("'%s.list_display[%d]', '%s' is a ManyToManyField which is not supported."

django/contrib/contenttypes/generic.py

@@ -59,7 +59,7 @@ class GenericForeignKey(object):
 
     def __get__(self, instance, instance_type=None):
         if instance is None:
-            raise AttributeError, u"%s must be accessed via instance" % self.name
+            return self
 
         try:
             return getattr(instance, self.cache_attr)
@@ -183,7 +183,7 @@ class ReverseGenericRelatedObjectsDescriptor(object):
 
     def __get__(self, instance, instance_type=None):
         if instance is None:
-            raise AttributeError, "Manager must be accessed via instance"
+            return self
 
         # This import is done here to avoid circular import importing this module
         from django.contrib.contenttypes.models import ContentType

django/db/models/fields/related.py

@@ -175,7 +175,7 @@ class SingleRelatedObjectDescriptor(object):
 
     def __get__(self, instance, instance_type=None):
         if instance is None:
-            raise AttributeError, "%s must be accessed via instance" % self.related.opts.object_name
+            return self
 
         try:
             return getattr(instance, self.cache_name)
@@ -223,7 +223,7 @@ class ReverseSingleRelatedObjectDescriptor(object):
 
     def __get__(self, instance, instance_type=None):
         if instance is None:
-            raise AttributeError, "%s must be accessed via instance" % self.field.name
+            return self
         cache_name = self.field.get_cache_name()
         try:
             return getattr(instance, cache_name)
@@ -287,7 +287,7 @@ class ForeignRelatedObjectsDescriptor(object):
 
     def __get__(self, instance, instance_type=None):
         if instance is None:
-            raise AttributeError, "Manager must be accessed via instance"
+            return self
 
         rel_field = self.related.field
         rel_model = self.related.model
@@ -500,7 +500,7 @@ class ManyRelatedObjectsDescriptor(object):
 
     def __get__(self, instance, instance_type=None):
         if instance is None:
-            raise AttributeError, "Manager must be accessed via instance"
+            return self
 
         # Dynamically create a class that subclasses the related
         # model's default manager.
@@ -545,7 +545,7 @@ class ReverseManyRelatedObjectsDescriptor(object):
 
     def __get__(self, instance, instance_type=None):
         if instance is None:
-            raise AttributeError, "Manager must be accessed via instance"
+            return self
 
         # Dynamically create a class that subclasses the related
         # model's default manager.