Refs #23941 -- Prevented incorrect rounding of DecimalField annotations on SQLite.

django/db/backends/sqlite3/operations.py

@@ -1,12 +1,13 @@
 import datetime
+import decimal
 import uuid
-from decimal import Decimal
 
 from django.conf import settings
 from django.core.exceptions import FieldError
 from django.db import utils
 from django.db.backends.base.operations import BaseDatabaseOperations
 from django.db.models import aggregates, fields
+from django.db.models.expressions import Col
 from django.utils import timezone
 from django.utils.dateparse import parse_date, parse_datetime, parse_time
 from django.utils.duration import duration_string
@@ -242,8 +243,12 @@ class DatabaseOperations(BaseDatabaseOperations):
 
     def convert_decimalfield_value(self, value, expression, connection):
         if value is not None:
+            if not isinstance(expression, Col):
+                # SQLite stores only 15 significant digits. Digits coming from
+                # float inaccuracy must be removed.
+                return decimal.Context(prec=15).create_decimal_from_float(value)
             value = expression.output_field.format_number(value)
-            value = Decimal(value)
+            return decimal.Decimal(value)
         return value
 
     def convert_uuidfield_value(self, value, expression, connection):

tests/annotations/tests.py

@@ -244,6 +244,20 @@ class NonAggregateAnnotationTestCase(TestCase):
                 sum_rating=Sum('rating')
             ).filter(sum_rating=F('nope')))
 
+    def test_decimal_annotation(self):
+        salary = Decimal(10) ** -Employee._meta.get_field('salary').decimal_places
+        Employee.objects.create(
+            first_name='Max',
+            last_name='Paine',
+            store=Store.objects.first(),
+            age=23,
+            salary=salary,
+        )
+        self.assertEqual(
+            Employee.objects.annotate(new_salary=F('salary') / 10).get().new_salary,
+            salary / 10,
+        )
+
     def test_filter_decimal_annotation(self):
         qs = Book.objects.annotate(new_price=F('price') + 1).filter(new_price=Decimal(31)).values_list('new_price')
         self.assertEqual(qs.get(), (Decimal(31),))