[2.2.x] 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.

Backport of ee6e93ec87 from master

django/db/models/expressions.py

@@ -372,7 +372,10 @@ 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,
@@ -839,6 +839,7 @@ class ExpressionsTests(TestCase):
         )
 
 
+@isolate_apps('expressions')
 class SimpleExpressionTests(SimpleTestCase):
 
     def test_equal(self):
@@ -852,6 +853,15 @@ 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(
@@ -863,6 +873,15 @@ 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

@@ -143,6 +143,7 @@ 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
@@ -225,3 +225,10 @@ 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

@@ -2345,7 +2345,7 @@ 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)