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.

2 files changed, 18 insertions, 7 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