Fixed #24986 -- Added support for annotations in DISTINCT queries.

AUTHORS

@@ -208,6 +208,7 @@ answer newbie questions, and generally made Django that much better:
     Dmitri Fedortchenko <zeraien@gmail.com>
     Dmitry Jemerov <intelliyole@gmail.com>
     dne@mayonnaise.net
+    Donald Harvey <donald@donaldharvey.co.uk>
     Donald Stufft <donald@stufft.io>
     Don Spaulding <donspauldingii@gmail.com>
     Doug Beck <doug@douglasbeck.com>
@@ -710,6 +711,7 @@ answer newbie questions, and generally made Django that much better:
     Tyler Tarabula <tyler.tarabula@gmail.com>
     Tyson Tate <tyson@fallingbullets.com>
     Unai Zalakain <unai@gisa-elkartea.org>
+    Valentina Mukhamedzhanova <umirra@gmail.com>
     valtron
     Vasiliy Stavenko <stavenko@gmail.com>
     Vasil Vangelovski

django/db/models/sql/compiler.py

@@ -548,6 +548,9 @@ class SQLCompiler(object):
             _, targets, alias, joins, path, _ = self._setup_joins(parts, opts, None)
             targets, alias, _ = self.query.trim_joins(targets, joins, path)
             for target in targets:
+                if name in self.query.annotation_select:
+                    result.append(name)
+                else:
                     result.append("%s.%s" % (qn(alias), qn2(target.column)))
         return result
 

django/db/models/sql/query.py

@@ -1292,9 +1292,15 @@ class Query(object):
             cur_names_with_path = (name, [])
             if name == 'pk':
                 name = opts.pk.name
+
+            field = None
             try:
                 field = opts.get_field(name)
+            except FieldDoesNotExist:
+                if name in self.annotation_select:
+                    field = self.annotation_select[name].output_field
 
+            if field is not None:
                 # Fields that contain one-to-many relations with a generic
                 # model (like a GenericForeignKey) cannot generate reverse
                 # relations and therefore cannot be used for reverse querying.
@@ -1305,8 +1311,11 @@ class Query(object):
                         "querying. If it is a GenericForeignKey, consider "
                         "adding a GenericRelation." % name
                     )
+                try:
                     model = field.model._meta.concrete_model
-            except FieldDoesNotExist:
+                except AttributeError:
+                    model = None
+            else:
                 # We didn't find the current field, so move position back
                 # one step.
                 pos -= 1

docs/releases/1.9.txt

@@ -462,6 +462,8 @@ Models
   :attr:`~django.db.models.SlugField.allow_unicode` argument to allow Unicode
   characters in slugs.
 
+* Added support for referencing annotations in ``QuerySet.distinct()``.
+
 CSRF
 ^^^^
 

tests/annotations/tests.py

@@ -8,7 +8,8 @@ from django.db.models import (
     F, BooleanField, CharField, Count, DateTimeField, ExpressionWrapper, Func,
     IntegerField, Sum, Value,
 )
-from django.test import TestCase
+from django.db.models.functions import Lower
+from django.test import TestCase, skipUnlessDBFeature
 from django.utils import six
 
 from .models import (
@@ -160,6 +161,40 @@ class NonAggregateAnnotationTestCase(TestCase):
         other_agg = Author.objects.aggregate(age_sum=Sum('age'))
         self.assertEqual(agg['otherage_sum'], other_agg['age_sum'])
 
+    @skipUnlessDBFeature('can_distinct_on_fields')
+    def test_distinct_on_with_annotation(self):
+        store = Store.objects.create(
+            name='test store',
+            original_opening=datetime.datetime.now(),
+            friday_night_closing=datetime.time(21, 00, 00),
+        )
+        names = [
+            'Theodore Roosevelt',
+            'Eleanor Roosevelt',
+            'Franklin Roosevelt',
+            'Ned Stark',
+            'Catelyn Stark',
+        ]
+        for name in names:
+            Employee.objects.create(
+                store=store,
+                first_name=name.split()[0],
+                last_name=name.split()[1],
+                age=30, salary=2000,
+            )
+
+        people = Employee.objects.annotate(
+            name_lower=Lower('last_name'),
+        ).distinct('name_lower')
+
+        self.assertEqual(set(p.last_name for p in people), {'Stark', 'Roosevelt'})
+        self.assertEqual(len(people), 2)
+
+        people2 = Employee.objects.annotate(
+            test_alias=F('store__name'),
+        ).distinct('test_alias')
+        self.assertEqual(len(people2), 1)
+
     def test_filter_annotation(self):
         books = Book.objects.annotate(
             is_book=Value(1, output_field=IntegerField())