magic-removal: Added support for QuerySet.latest() and Manager.latest(), and updated unit tests.

git-svn-id: http://code.djangoproject.com/svn/django/branches/magic-removal@2260 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/db/models/fields/related.py

@@ -126,12 +126,7 @@ class ManyRelatedObjectsDescriptor(object):
         else:
             manager.core_filters = {'%s__%s__exact' % (rel_field.name, instance_type._meta.pk.name): instance._get_pk_val()}
 
-        # Prepare the manager.
-        # TODO: Fix this hack?
-        # We're setting manager.model here because manager._prepare() expects
-        # that manager.model is set. This is slightly hackish.
         manager.model = self.related.model
-        manager._prepare()
 
         return manager
 
@@ -194,13 +189,7 @@ class ReverseManyRelatedObjectsDescriptor(object):
             add.alters_data = True
 
         manager = RelatedManager()
-
-        # Prepare the manager.
-        # TODO: Fix this hack?
-        # We're setting manager.model here because manager._prepare() expects
-        # that manager.model is set. This is slightly hackish.
         manager.model = self.rel_model
-        manager._prepare()
 
         return manager
 

django/db/models/manager.py

@@ -16,7 +16,6 @@ def ensure_default_manager(sender):
         if hasattr(cls, 'objects'):
             raise ValueError, "Model %s must specify a custom Manager, because it has a field named 'objects'" % name
         cls.add_to_class('objects', Manager())
-        cls.objects._prepare()
 
 dispatcher.connect(ensure_default_manager, signal=signals.class_prepared)
 
@@ -31,23 +30,13 @@ class Manager(object):
         Manager.creation_counter += 1
         self.model = None
 
-    def _prepare(self):
-        if self.model._meta.get_latest_by:
-            self.get_latest = self.__get_latest
-
     def contribute_to_class(self, model, name):
         # TODO: Use weakref because of possible memory leak / circular reference.
         self.model = model
-        dispatcher.connect(self._prepare, signal=signals.class_prepared, sender=model)
         setattr(model, name, ManagerDescriptor(self))
         if not hasattr(model, '_default_manager') or self.creation_counter < model._default_manager.creation_counter:
             model._default_manager = self
 
-    def __get_latest(self, *args, **kwargs):
-        kwargs['order_by'] = ('-' + self.model._meta.get_latest_by,)
-        kwargs['limit'] = 1
-        return self.get_object(*args, **kwargs)
-
     #######################
     # PROXIES TO QUERYSET #
     #######################
@@ -89,6 +78,9 @@ class Manager(object):
     def iterator(self, *args, **kwargs):
         return self.get_query_set().iterator(*args, **kwargs)
 
+    def latest(self, *args, **kwargs):
+        return self.get_query_set().latest(*args, **kwargs)
+
     def order_by(self, *args, **kwargs):
         return self.get_query_set().order_by(*args, **kwargs)
 

django/db/models/query.py

@@ -162,6 +162,15 @@ class QuerySet(object):
         assert len(obj_list) == 1, "get() returned more than one %s -- it returned %s! Lookup parameters were %s" % (self.model._meta.object_name, len(obj_list), kwargs)
         return obj_list[0]
 
+    def latest(self, field_name=None):
+        """
+        Returns the latest object, according to the model's 'get_latest_by'
+        option or optional given field_name.
+        """
+        latest_by = field_name or self.model._meta.get_latest_by
+        assert bool(latest_by), "latest() requires either a field_name parameter or 'get_latest_by' in the model"
+        return self._clone(_limit=1, _order_by=('-'+latest_by,)).get()
+
     def delete(self, *args, **kwargs):
         """
         Deletes the records with the given kwargs. If no kwargs are given,

tests/modeltests/get_latest/models.py

@@ -12,32 +12,68 @@ from django.db import models
 
 class Article(models.Model):
     headline = models.CharField(maxlength=100)
-    pub_date = models.DateTimeField()
+    pub_date = models.DateField()
+    expire_date = models.DateField()
     class Meta:
         get_latest_by = 'pub_date'
 
     def __repr__(self):
         return self.headline
 
+class Person(models.Model):
+    name = models.CharField(maxlength=30)
+    birthday = models.DateField()
+
+    # Note that this model doesn't have "get_latest_by" set.
+
+    def __repr__(self):
+        return self.name
+
 API_TESTS = """
 # Because no Articles exist yet, get_latest() raises ArticleDoesNotExist.
->>> Article.objects.get_latest()
+>>> Article.objects.latest()
 Traceback (most recent call last):
     ...
-DoesNotExist: Article does not exist for {'order_by': ('-pub_date',), 'limit': 1}
+DoesNotExist: Article does not exist for ...
 
 # Create a couple of Articles.
 >>> from datetime import datetime
->>> a1 = Article(id=None, headline='Article 1', pub_date=datetime(2005, 7, 26))
+>>> a1 = Article(headline='Article 1', pub_date=datetime(2005, 7, 26), expire_date=datetime(2005, 9, 1))
 >>> a1.save()
->>> a2 = Article(id=None, headline='Article 2', pub_date=datetime(2005, 7, 27))
+>>> a2 = Article(headline='Article 2', pub_date=datetime(2005, 7, 27), expire_date=datetime(2005, 7, 28))
 >>> a2.save()
->>> a3 = Article(id=None, headline='Article 3', pub_date=datetime(2005, 7, 27))
+>>> a3 = Article(headline='Article 3', pub_date=datetime(2005, 7, 27), expire_date=datetime(2005, 8, 27))
 >>> a3.save()
->>> a4 = Article(id=None, headline='Article 4', pub_date=datetime(2005, 7, 28))
+>>> a4 = Article(headline='Article 4', pub_date=datetime(2005, 7, 28), expire_date=datetime(2005, 7, 30))
 >>> a4.save()
 
 # Get the latest Article.
->>> Article.objects.get_latest()
+>>> Article.objects.latest()
 Article 4
+
+# Get the latest Article that matches certain filters.
+>>> Article.objects.filter(pub_date__lt=datetime(2005, 7, 27)).latest()
+Article 1
+
+# Pass a custom field name to latest() to change the field that's used to
+# determine the latest object.
+>>> Article.objects.latest('expire_date')
+Article 1
+
+>>> Article.objects.filter(pub_date__gt=datetime(2005, 7, 26)).latest('expire_date')
+Article 3
+
+# You can still use latest() with a model that doesn't have "get_latest_by"
+# set -- just pass in the field name manually.
+>>> p1 = Person(name='Ralph', birthday=datetime(1950, 1, 1))
+>>> p1.save()
+>>> p2 = Person(name='Stephanie', birthday=datetime(1960, 2, 3))
+>>> p2.save()
+>>> Person.objects.latest()
+Traceback (most recent call last):
+    ...
+AssertionError: latest() requires either a field_name parameter or 'get_latest_by' in the model
+
+>>> Person.objects.latest('birthday')
+Stephanie
 """