[1.0.X] Use plain model.Manager, or suitable proxy, for model saving.

We can't use the default manager in Model.save_base(), since we need to
retrieve existing objects which might be filtered out by that manager. We now
always use a plain Manager instance at that point (or something that can
replace it, such as a GeoManager), making all existing rows in the
database visible to the saving code.

The logic for detecting a "suitable replacement" plain base is the same as for
related fields: if the use_for_related_fields is set on the manager subclass,
we can use it. The general requirement here is that we want a base class that
returns the appropriate QuerySet subclass, but does not restrict the rows
returned.

Fixed #8990, #9527.

Refs #2698 (which is not fixed by this change, but it's the first part of a
larger change to fix that bug.)

Backport of r10056 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10059 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/custom_managers_regress/models.py

@@ -0,0 +1,38 @@
+"""
+Regression tests for custom manager classes.
+"""
+
+from django.db import models
+
+class RestrictedManager(models.Manager):
+    """
+    A manager that filters out non-public instances.
+    """
+    def get_query_set(self):
+        return super(RestrictedManager, self).get_query_set().filter(is_public=True)
+
+class RestrictedClass(models.Model):
+    name = models.CharField(max_length=50)
+    is_public = models.BooleanField(default=False)
+
+    objects = RestrictedManager()
+    plain_manager = models.Manager()
+
+    def __unicode__(self):
+        return self.name
+
+__test__ = {"tests": """
+Even though the default manager filters out some records, we must still be able
+to save (particularly, save by updating existing records) those filtered
+instances. This is a regression test for #FIXME.
+>>> obj = RestrictedClass.objects.create(name="hidden")
+>>> obj.name = "still hidden"
+>>> obj.save()
+
+# If the hidden object wasn't seen during the save process, there would now be
+# two objects in the database.
+>>> RestrictedClass.plain_manager.count()
+1
+
+"""
+}