Fixed #30628 -- Adjusted expression identity to differentiate bound fields.

Expressions referring to different bound fields should not be
considered equal.

Thanks Julien Enselme for the detailed report.

Regression in bc7e288ca9.

django/db/models/expressions.py

@@ -376,7 +376,10 @@ class BaseExpression:
         identity = [self.__class__]
         for arg, value in arguments:
             if isinstance(value, fields.Field):
-                value = type(value)
+                if value.name and value.model:
+                    value = (value.model._meta.label, value.name)
+                else:
+                    value = type(value)
             else:
                 value = make_hashable(value)
             identity.append((arg, value))

docs/releases/2.2.4.txt

@@ -9,4 +9,6 @@ Django 2.2.4 fixes several bugs in 2.2.3.
 Bugfixes
 ========
 
-* ...
+* Fixed a regression in Django 2.2 when ordering a ``QuerySet.union()``,
+  ``intersection()``, or ``difference()`` by a field type present more than
+  once results in the wrong ordering being used (:ticket:`30628`).

tests/expressions/tests.py

@@ -21,7 +21,7 @@ from django.db.models.functions import (
 from django.db.models.sql import constants
 from django.db.models.sql.datastructures import Join
 from django.test import SimpleTestCase, TestCase, skipUnlessDBFeature
-from django.test.utils import Approximate
+from django.test.utils import Approximate, isolate_apps
 
 from .models import (
     UUID, UUIDPK, Company, Employee, Experiment, Number, RemoteEmployee,
@@ -898,6 +898,7 @@ class ExpressionsTests(TestCase):
         )
 
 
+@isolate_apps('expressions')
 class SimpleExpressionTests(SimpleTestCase):
 
     def test_equal(self):
@@ -911,6 +912,15 @@ class SimpleExpressionTests(SimpleTestCase):
             Expression(models.CharField())
         )
 
+        class TestModel(models.Model):
+            field = models.IntegerField()
+            other_field = models.IntegerField()
+
+        self.assertNotEqual(
+            Expression(TestModel._meta.get_field('field')),
+            Expression(TestModel._meta.get_field('other_field')),
+        )
+
     def test_hash(self):
         self.assertEqual(hash(Expression()), hash(Expression()))
         self.assertEqual(
@@ -922,6 +932,15 @@ class SimpleExpressionTests(SimpleTestCase):
             hash(Expression(models.CharField())),
         )
 
+        class TestModel(models.Model):
+            field = models.IntegerField()
+            other_field = models.IntegerField()
+
+        self.assertNotEqual(
+            hash(Expression(TestModel._meta.get_field('field'))),
+            hash(Expression(TestModel._meta.get_field('other_field'))),
+        )
+
 
 class ExpressionsNumericTests(TestCase):
 

tests/queries/models.py

@@ -148,6 +148,7 @@ class Cover(models.Model):
 
 class Number(models.Model):
     num = models.IntegerField()
+    other_num = models.IntegerField(null=True)
 
     def __str__(self):
         return str(self.num)

tests/queries/test_qs_combinators.py

@@ -9,7 +9,7 @@ from .models import Number, ReservedName
 class QuerySetSetOperationTests(TestCase):
     @classmethod
     def setUpTestData(cls):
-        Number.objects.bulk_create(Number(num=i) for i in range(10))
+        Number.objects.bulk_create(Number(num=i, other_num=10 - i) for i in range(10))
 
     def number_transform(self, value):
         return value.num
@@ -251,3 +251,10 @@ class QuerySetSetOperationTests(TestCase):
         qs1 = Number.objects.all()
         qs2 = Number.objects.intersection(Number.objects.filter(num__gt=1))
         self.assertEqual(qs1.difference(qs2).count(), 2)
+
+    def test_order_by_same_type(self):
+        qs = Number.objects.all()
+        union = qs.union(qs)
+        numbers = list(range(10))
+        self.assertNumbersEqual(union.order_by('num'), numbers)
+        self.assertNumbersEqual(union.order_by('other_num'), reversed(numbers))

tests/queries/tests.py

@@ -2335,7 +2335,7 @@ class ValuesQuerysetTests(TestCase):
         qs = Number.objects.extra(select={'num2': 'num+1'}).annotate(Count('id'))
         values = qs.values_list(named=True).first()
         self.assertEqual(type(values).__name__, 'Row')
-        self.assertEqual(values._fields, ('num2', 'id', 'num', 'id__count'))
+        self.assertEqual(values._fields, ('num2', 'id', 'num', 'other_num', 'id__count'))
         self.assertEqual(values.num, 72)
         self.assertEqual(values.num2, 73)
         self.assertEqual(values.id__count, 1)