Ticket #17813: first_latest_with_tests.patch

django/db/models/manager.py

@@ -160 +160 @@
     def iterator(self, *args, **kwargs):
         return self.get_query_set().iterator(*args, **kwargs)
 
+    def first(self, *args, **kwargs):
+        return self.get_query_set().first(*args, **kwargs)
+
     def latest(self, *args, **kwargs):
         return self.get_query_set().latest(*args, **kwargs)
 

django/db/models/query.py

@@ -458 +458 @@
                     # Re-raise the IntegrityError with its original traceback.
                     raise exc_info[1], None, exc_info[2]
 
-    def latest(self, field_name=None):
+    def _first_or_latest(self, field_name=None, direction="-"):
         """
         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"
+        order_by = field_name or self.model._meta.get_latest_by
+        assert bool(order_by), \
+               "_first_or_latest() requires either a field_name parameter or 'get_latest_by' in the model"
         assert self.query.can_filter(), \
                 "Cannot change a query once a slice has been taken."
         obj = self._clone()
         obj.query.set_limits(high=1)
         obj.query.clear_ordering()
-        obj.query.add_ordering('-%s' % latest_by)
+        obj.query.add_ordering('%s%s' % (direction, order_by))     
         return obj.get()
+    
+    def first(self, field_name=None):
+        return self._first_or_latest(field_name=field_name, direction="")
+    
+    def latest(self, field_name=None):
+        return self._first_or_latest(field_name=field_name, direction="-")
+    
 
     def in_bulk(self, id_list):
         """

tests/modeltests/get_latest/tests.py

@@ -8 +8 @@
 
 
 class LatestTests(TestCase):
+    def test_first(self):
+        # Because no Articles exist yet, first() raises ArticleDoesNotExist.
+        self.assertRaises(Article.DoesNotExist, Article.objects.first)
+
+        a1 = Article.objects.create(
+            headline="Article 1", pub_date=datetime(2005, 7, 26),
+            expire_date=datetime(2005, 9, 1)
+        )
+        a2 = Article.objects.create(
+            headline="Article 2", pub_date=datetime(2005, 7, 27),
+            expire_date=datetime(2005, 7, 28)
+        )
+        a3 = Article.objects.create(
+            headline="Article 3", pub_date=datetime(2005, 7, 28),
+            expire_date=datetime(2005, 8, 27)
+        )
+        a4 = Article.objects.create(
+            headline="Article 4", pub_date=datetime(2005, 7, 28),
+            expire_date=datetime(2005, 7, 30)
+        )
+
+        # Get the first Article.
+        self.assertEqual(Article.objects.first(), a1)
+        # Get the first Article that matches certain filters.
+        self.assertEqual(
+            Article.objects.filter(pub_date__gt=datetime(2005, 7, 26)).first(),
+            a2
+        )
+
+        # Pass a custom field name to first() to change the field that's used
+        # to determine the first object.
+        self.assertEqual(Article.objects.first('expire_date'), a2)
+        self.assertEqual(
+            Article.objects.filter(pub_date__gt=datetime(2005, 7, 26)).first('expire_date'),
+            a2,
+        )
+
+        # Ensure that first() overrides any other ordering specified on the query. Refs #11283.
+        self.assertEqual(Article.objects.order_by('id').first(), a1)
+
     def test_latest(self):
         # Because no Articles exist yet, latest() raises ArticleDoesNotExist.
         self.assertRaises(Article.DoesNotExist, Article.objects.latest)