Fixed #17813 -- Added a .earliest() method to QuerySet

Thanks a lot to everybody participating in developing this feature.
The patch was developed by multiple people, at least Trac aliases
tonnzor, jimmysong, Fandekasp and slurms.

Stylistic changes added by committer.

9 files changed, 164 insertions, 77 deletions

diff --git a/django/db/models/manager.py b/django/db/models/manager.py
index da6523c89a..816f6194e3 100644
--- a/django/db/models/manager.py
+++ b/django/db/models/manager.py
@@ -172,6 +172,9 @@ class Manager(object):
     def iterator(self, *args, **kwargs):
         return self.get_query_set().iterator(*args, **kwargs)
 
+    def earliest(self, *args, **kwargs):
+        return self.get_query_set().earliest(*args, **kwargs)
+
     def latest(self, *args, **kwargs):
         return self.get_query_set().latest(*args, **kwargs)
 
diff --git a/django/db/models/query.py b/django/db/models/query.py
index bdb6d48adc..1c9a68a677 100644
--- a/django/db/models/query.py
+++ b/django/db/models/query.py
@@ -29,6 +29,7 @@ REPR_OUTPUT_SIZE = 20
 # Pull into this namespace for backwards compatibility.
 EmptyResultSet = sql.EmptyResultSet
 
+
 class QuerySet(object):
     """
     Represents a lazy database lookup for a set of objects.
@@ -487,21 +488,28 @@ class QuerySet(object):
                     # Re-raise the IntegrityError with its original traceback.
                     six.reraise(*exc_info)
 
-    def latest(self, field_name=None):
+    def _earliest_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.
+        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 getattr(self.model._meta, 'get_latest_by')
+        assert bool(order_by), "earliest() and latest() require 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."
+            "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 earliest(self, field_name=None):
+        return self._earliest_or_latest(field_name=field_name, direction="")
+
+    def latest(self, field_name=None):
+        return self._earliest_or_latest(field_name=field_name, direction="-")
+
     def in_bulk(self, id_list):
         """
         Returns a dictionary mapping each of the given IDs to the object with
diff --git a/docs/ref/models/options.txt b/docs/ref/models/options.txt
index b349197a5b..21265d6313 100644
--- a/docs/ref/models/options.txt
+++ b/docs/ref/models/options.txt
@@ -86,7 +86,8 @@ Django quotes column and table names behind the scenes.
     The name of an orderable field in the model, typically a :class:`DateField`,
     :class:`DateTimeField`, or :class:`IntegerField`. This specifies the default
     field to use in your model :class:`Manager`'s
-    :meth:`~django.db.models.query.QuerySet.latest` method.
+    :meth:`~django.db.models.query.QuerySet.latest` and
+    :meth:`~django.db.models.query.QuerySet.earliest` methods.
 
     Example::
 
diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt
index 71049703c9..1f59ecb4f4 100644
--- a/docs/ref/models/querysets.txt
+++ b/docs/ref/models/querysets.txt
@@ -1477,14 +1477,23 @@ This example returns the latest ``Entry`` in the table, according to the
 
 If your model's :ref:`Meta <meta-options>` specifies
 :attr:`~django.db.models.Options.get_latest_by`, you can leave off the
-``field_name`` argument to ``latest()``. Django will use the field specified
-in :attr:`~django.db.models.Options.get_latest_by` by default.
+``field_name`` argument to ``earliest()`` or ``latest()``. Django will use the
+field specified in :attr:`~django.db.models.Options.get_latest_by` by default.
 
-Like :meth:`get()`, ``latest()`` raises
-:exc:`~django.core.exceptions.DoesNotExist` if there is no object with the given
-parameters.
+Like :meth:`get()`, ``earliest()`` and ``latest()`` raise
+:exc:`~django.core.exceptions.DoesNotExist` if there is no object with the
+given parameters.
+
+Note that ``earliest()`` and ``latest()`` exist purely for convenience and
+readability.
+
+earliest
+~~~~~~~~
+
+.. method:: earliest(field_name=None)
 
-Note ``latest()`` exists purely for convenience and readability.
+Works otherwise like :meth:`~django.db.models.query.QuerySet.latest` except
+the direction is changed.
 
 aggregate
 ~~~~~~~~~
diff --git a/docs/releases/1.6.txt b/docs/releases/1.6.txt
index dcf6f2604a..89d7bb3c05 100644
--- a/docs/releases/1.6.txt
+++ b/docs/releases/1.6.txt
@@ -28,6 +28,9 @@ Minor features
   undefined if the given ``QuerySet`` isn't ordered and there are more than
   one ordered values to compare against.
 
+* Added :meth:`~django.db.models.query.QuerySet.earliest` for symmetry with
+  :meth:`~django.db.models.query.QuerySet.latest`.
+
 Backwards incompatible changes in 1.6
 =====================================
 
diff --git a/tests/modeltests/get_latest/__init__.py b/tests/modeltests/get_earliest_or_latest/__init__.py
index e69de29bb2..e69de29bb2 100644
--- a/tests/modeltests/get_latest/__init__.py
+++ b/tests/modeltests/get_earliest_or_latest/__init__.py
diff --git a/tests/modeltests/get_latest/models.py b/tests/modeltests/get_earliest_or_latest/models.py
index fe594dd802..2453eaaccd 100644
--- a/tests/modeltests/get_latest/models.py
+++ b/tests/modeltests/get_earliest_or_latest/models.py
@@ -9,10 +9,8 @@ farthest into the future."
 """
 
 from django.db import models
-from django.utils.encoding import python_2_unicode_compatible
 
 
-@python_2_unicode_compatible
 class Article(models.Model):
     headline = models.CharField(max_length=100)
     pub_date = models.DateField()
@@ -20,15 +18,15 @@ class Article(models.Model):
     class Meta:
         get_latest_by = 'pub_date'
 
-    def __str__(self):
+    def __unicode__(self):
         return self.headline
 
-@python_2_unicode_compatible
+
 class Person(models.Model):
     name = models.CharField(max_length=30)
     birthday = models.DateField()
 
     # Note that this model doesn't have "get_latest_by" set.
 
-    def __str__(self):
+    def __unicode__(self):
         return self.name
diff --git a/tests/modeltests/get_earliest_or_latest/tests.py b/tests/modeltests/get_earliest_or_latest/tests.py
new file mode 100644
index 0000000000..6317a0974c
--- /dev/null
+++ b/tests/modeltests/get_earliest_or_latest/tests.py
@@ -0,0 +1,123 @@
+from __future__ import absolute_import
+
+from datetime import datetime
+
+from django.test import TestCase
+
+from .models import Article, Person
+
+
+class EarliestOrLatestTests(TestCase):
+    """Tests for the earliest() and latest() objects methods"""
+
+    def tearDown(self):
+        """Makes sure Article has a get_latest_by"""
+        if not Article._meta.get_latest_by:
+            Article._meta.get_latest_by = 'pub_date'
+
+    def test_earliest(self):
+        # Because no Articles exist yet, earliest() raises ArticleDoesNotExist.
+        self.assertRaises(Article.DoesNotExist, Article.objects.earliest)
+
+        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 earliest Article.
+        self.assertEqual(Article.objects.earliest(), a1)
+        # Get the earliest Article that matches certain filters.
+        self.assertEqual(
+            Article.objects.filter(pub_date__gt=datetime(2005, 7, 26)).earliest(),
+            a2
+        )
+
+        # Pass a custom field name to earliest() to change the field that's used
+        # to determine the earliest object.
+        self.assertEqual(Article.objects.earliest('expire_date'), a2)
+        self.assertEqual(Article.objects.filter(
+            pub_date__gt=datetime(2005, 7, 26)).earliest('expire_date'), a2)
+
+        # Ensure that earliest() overrides any other ordering specified on the
+        # query. Refs #11283.
+        self.assertEqual(Article.objects.order_by('id').earliest(), a1)
+
+        # Ensure that error is raised if the user forgot to add a get_latest_by
+        # in the Model.Meta
+        Article.objects.model._meta.get_latest_by = None
+        self.assertRaisesMessage(
+            AssertionError,
+            "earliest() and latest() require either a field_name parameter or "
+            "'get_latest_by' in the model",
+            lambda: Article.objects.earliest(),
+        )
+
+    def test_latest(self):
+        # Because no Articles exist yet, latest() raises ArticleDoesNotExist.
+        self.assertRaises(Article.DoesNotExist, Article.objects.latest)
+
+        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, 27),
+            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 latest Article.
+        self.assertEqual(Article.objects.latest(), a4)
+        # Get the latest Article that matches certain filters.
+        self.assertEqual(
+            Article.objects.filter(pub_date__lt=datetime(2005, 7, 27)).latest(),
+            a1
+        )
+
+        # Pass a custom field name to latest() to change the field that's used
+        # to determine the latest object.
+        self.assertEqual(Article.objects.latest('expire_date'), a1)
+        self.assertEqual(
+            Article.objects.filter(pub_date__gt=datetime(2005, 7, 26)).latest('expire_date'),
+            a3,
+        )
+
+        # Ensure that latest() overrides any other ordering specified on the query. Refs #11283.
+        self.assertEqual(Article.objects.order_by('id').latest(), a4)
+
+        # Ensure that error is raised if the user forgot to add a get_latest_by
+        # in the Model.Meta
+        Article.objects.model._meta.get_latest_by = None
+        self.assertRaisesMessage(
+            AssertionError,
+            "earliest() and latest() require either a field_name parameter or "
+            "'get_latest_by' in the model",
+            lambda: Article.objects.latest(),
+        )
+
+    def test_latest_manual(self):
+        # 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.objects.create(name="Ralph", birthday=datetime(1950, 1, 1))
+        p2 = Person.objects.create(name="Stephanie", birthday=datetime(1960, 2, 3))
+        self.assertRaises(AssertionError, Person.objects.latest)
+        self.assertEqual(Person.objects.latest("birthday"), p2)
diff --git a/tests/modeltests/get_latest/tests.py b/tests/modeltests/get_latest/tests.py
deleted file mode 100644
index 948af6045a..0000000000
--- a/tests/modeltests/get_latest/tests.py
+++ /dev/null
@@ -1,58 +0,0 @@
-from __future__ import absolute_import
-
-from datetime import datetime
-
-from django.test import TestCase
-
-from .models import Article, Person
-
-
-class LatestTests(TestCase):
-    def test_latest(self):
-        # Because no Articles exist yet, latest() raises ArticleDoesNotExist.
-        self.assertRaises(Article.DoesNotExist, Article.objects.latest)
-
-        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, 27),
-            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 latest Article.
-        self.assertEqual(Article.objects.latest(), a4)
-        # Get the latest Article that matches certain filters.
-        self.assertEqual(
-            Article.objects.filter(pub_date__lt=datetime(2005, 7, 27)).latest(),
-            a1
-        )
-
-        # Pass a custom field name to latest() to change the field that's used
-        # to determine the latest object.
-        self.assertEqual(Article.objects.latest('expire_date'), a1)
-        self.assertEqual(
-            Article.objects.filter(pub_date__gt=datetime(2005, 7, 26)).latest('expire_date'),
-            a3,
-        )
-
-        # Ensure that latest() overrides any other ordering specified on the query. Refs #11283.
-        self.assertEqual(Article.objects.order_by('id').latest(), a4)
-
-    def test_latest_manual(self):
-        # 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.objects.create(name="Ralph", birthday=datetime(1950, 1, 1))
-        p2 = Person.objects.create(name="Stephanie", birthday=datetime(1960, 2, 3))
-        self.assertRaises(AssertionError, Person.objects.latest)
-
-        self.assertEqual(Person.objects.latest("birthday"), p2)