Add fix for when _default_manager is a custom TreeManager and new tes…

…ts for custom TreeManagers.

Squashed commit of the following:

commit d55f90c8f0b0b6c90a91ba04b1db1e34af099593
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 02:32:20 2015 +0200

    re-enable _default_manager and remove test that fails for some other reason on django 1.4 django-mptt/django-mptt#371

commit 3939f182564c2d1b32a70efb7a5c910234da3887
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 02:20:58 2015 +0200

    Oh hi Travis, can you check this again to see how Django 1.4 likes _default_manager ?

commit 17957e03d2b6f9abbf7db890914194489af2929e
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 02:09:20 2015 +0200

    also assert that the classic version of .none() is compatible with the custom manager's queryset

commit 1cf707d0dae042387f3fae1e34739860f1dbdf2d
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 01:59:22 2015 +0200

    fix for django-mptt/django-mptt#371 by customizing test to behave differently if it's pre django 1.6

commit fcf90deeaf1f4e4d4a3bb9e8be265cd4e475d576
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 01:47:20 2015 +0200

    Re-add _default_manager but uncomment test that's generally failing on django 1.4

commit 073698bf2f13b5ab3b77916ce434a46a183c83f6
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 01:26:59 2015 +0200

    Hi Travis, please test if this works with Django 1.4 because it didnt B4

commit 04308a02f3a0fb2b3e2e9a8a55593de330c3aaaa
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 01:13:41 2015 +0200

    Renaming custom manager in doctests

commit 92737e9890babe7f310ad0bd4b0594d49c000eb8
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 01:04:19 2015 +0200

    Add optimization: If conventional "objects" attr exists, just use that and don't iterate everything else, also fixes django-mptt/django-mptt#369

commit 2b47ffd611158fa91c44398e584b2c5f1f1e96bf
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 01:03:42 2015 +0200

    Add test cases that fail when using _default_manager and objects django-mptt/django-mptt#369

commit 1ba49283070e2fda7d00bdd2680a0f9a039c890f
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 01:02:25 2015 +0200

    Add a custom method and a _default_manager that points to "objects" to reflect a practice that may or may not exist out there in the wild django-mptt/django-mptt#369

commit 00933d01a3974c088330fb77bfeb7e65dbecf185
Author: Benjamin Bach <benjaoming@gmail.com>
Date:   Thu Apr 23 01:01:56 2015 +0200

    add a single row on the Person test model

mptt/models.py

@@ -327,21 +327,27 @@ def register(meta, cls, **kwargs):
 
                 # make sure we have a tree manager somewhere
                 tree_manager = None
-                for attr in sorted(dir(cls)):
-                    try:
-                        # HACK: avoid using getattr(cls, attr)
-                        # because it calls __get__ on descriptors, which can cause nasty side effects
-                        # with more inconsiderate apps.
-                        # (e.g. django-tagging's TagField is a descriptor which can do db queries on getattr)
-                        # ( ref: http://stackoverflow.com/questions/27790344 )
-                        obj = cls.__dict__[attr]
-                    except KeyError:
-                        continue
-                    if isinstance(obj, TreeManager):
-                        tree_manager = obj
-                        # prefer any locally defined manager (i.e. keep going if not local)
-                        if obj.model is cls:
-                            break
+                attrs = dir(cls)
+                if "objects" in attrs and isinstance(cls.objects, TreeManager):
+                    tree_manager = cls.objects
+
+                # Go look for it somewhere else
+                else:
+                    for attr in sorted(attrs):
+                        try:
+                            # HACK: avoid using getattr(cls, attr)
+                            # because it calls __get__ on descriptors, which can cause nasty side effects
+                            # with more inconsiderate apps.
+                            # (e.g. django-tagging's TagField is a descriptor which can do db queries on getattr)
+                            # ( ref: http://stackoverflow.com/questions/27790344 )
+                            obj = cls.__dict__[attr]
+                        except KeyError:
+                            continue
+                        if isinstance(obj, TreeManager):
+                            tree_manager = obj
+                            # prefer any locally defined manager (i.e. keep going if not local)
+                            if obj.model is cls:
+                                break
                 if tree_manager and tree_manager.model is not cls:
                     tree_manager = tree_manager._copy_to_model(cls)
                 elif tree_manager is None:

tests/myapp/doctests.txt

@@ -208,11 +208,11 @@
 
 # TreeManager Methods #########################################################
 # check that tree manager is the explicitly defined tree manager for Person
->>> Person._tree_manager == Person.my_tree_manager
+>>> Person._tree_manager == Person.objects
 True
 
 # managers of non-abstract bases don't get inherited, so:
->>> Student._tree_manager == Student.my_tree_manager
+>>> Student._tree_manager == Student.objects
 False
 
 >>> Student._tree_manager == Person._tree_manager
@@ -1554,7 +1554,7 @@ ValueError: Cannot insert a node which has already been saved.
 >>> jane = Student.objects.create(name='Jane', parent=jeff)
 >>> joe = Person.objects.create(name='Joe', parent=jane)
 >>> julie = Student.objects.create(name='Julie', parent=jess)
->>> print_tree_details(Person.my_tree_manager.all())
+>>> print_tree_details(Person.objects.all())
 1 - 1 0 1 6
 2 1 1 1 2 3
 3 1 1 1 4 5

tests/myapp/fixtures/persons.json

@@ -0,0 +1,14 @@
+[
+  {
+    "pk": 1, 
+    "model": "myapp.person", 
+    "fields": {
+      "rght": 16, 
+      "name": "John Doe", 
+      "parent": null, 
+      "level": 0, 
+      "lft": 1, 
+      "tree_id": 1
+    }
+  }
+]

tests/myapp/models.py

@@ -3,16 +3,27 @@
 from django.db import models
 from django.db.models.signals import pre_save
 from django.utils.encoding import python_2_unicode_compatible
+from django import VERSION as DJANGO_VERSION
+
 
 import mptt
 from mptt.fields import TreeForeignKey, TreeOneToOneField, TreeManyToManyField
 from mptt.models import MPTTModel
 from mptt.managers import TreeManager
-from django.db.models.query import QuerySet
+from django.db.models.query import QuerySet, EmptyQuerySet
 
 
 class CustomTreeQueryset(QuerySet):
-    pass
+
+    def custom_method(self):
+        pass
+
+
+class CustomEmptyTreeQueryset(EmptyQuerySet):
+    """This is only used pre Django 1.6"""
+
+    def custom_method(self):
+        pass
 
 
 class CustomTreeManager(TreeManager):
@@ -23,6 +34,16 @@ def get_queryset(self):
         # Django 1.8 removed the fallbacks here.
         return CustomTreeQueryset(model=self.model, using=self._db)
 
+    def get_empty_query_set(self):
+        # Pre 1.6 django, we needed a custom inheritor of EmptyQuerySet
+        # to pass custom methods. However, 1.6 introduced that EmptyQuerySet
+        # cannot be instantiated but instead passes through the methods
+        # of the custom QuerySet.
+        # See: https://code.djangoproject.com/ticket/22817
+        if DJANGO_VERSION < (1, 6):
+            return CustomEmptyTreeQueryset(model=self.model)
+        return self.get_queryset().none()
+
 
 @python_2_unicode_compatible
 class Category(MPTTModel):
@@ -124,7 +145,10 @@ class Person(MPTTModel):
     parent = TreeForeignKey('self', null=True, blank=True, related_name='children')
 
     # just testing it's actually possible to override the tree manager
-    my_tree_manager = CustomTreeManager()
+    objects = CustomTreeManager()
+
+    # This line is set because of https://github.com/django-mptt/django-mptt/issues/369
+    _default_manager = objects
 
     def __str__(self):
         return self.name

tests/myapp/tests.py

@@ -1126,7 +1126,8 @@ def test_move_root_to_child(self):
 
 class ManagerTests(TreeTestCase):
     fixtures = ['categories.json',
-                'genres.json']
+                'genres.json',
+                'persons.json']
 
     def test_all_managers_are_different(self):
         # all tree managers should be different. otherwise, possible infinite recursion.
@@ -1234,8 +1235,16 @@ def test_custom_querysets(self):
         """
         Test that a custom manager also provides custom querysets.
         """
-
+        
         self.assertTrue(isinstance(Person.objects.all(), CustomTreeQueryset))
+        self.assertTrue(isinstance(Person.objects.all()[0].get_children(), CustomTreeQueryset))
+        self.assertTrue(hasattr(Person.objects.none(), 'custom_method'))
+
+        # In Django 1.4, we would have had a custom type CustomEmptyTreeQueryset
+        # but this was abandoned in later versions. However, the best method is
+        # to just test if the custom method is available.
+        # self.assertTrue(hasattr(Person.objects.all()[0].get_children().none(), 'custom_method'))
+
         self.assertEqual(
             type(Person.objects.all()),
             type(Person.objects.root_nodes())