Refs #28643 -- Added math database functions.

Thanks Nick Pope for much review.

tests/db_functions/math/test_round.py

@@ -0,0 +1,50 @@
+from decimal import Decimal
+
+from django.db.models import DecimalField
+from django.db.models.functions import Round
+from django.test import TestCase
+
+from ..models import DecimalModel, FloatModel, IntegerModel
+
+
+class RoundTests(TestCase):
+
+    def test_decimal(self):
+        DecimalModel.objects.create(n1=Decimal('-12.9'), n2=Decimal('0.6'))
+        obj = DecimalModel.objects.annotate(n1_round=Round('n1'), n2_round=Round('n2')).first()
+        self.assertIsInstance(obj.n1_round, Decimal)
+        self.assertIsInstance(obj.n2_round, Decimal)
+        self.assertAlmostEqual(obj.n1_round, round(obj.n1))
+        self.assertAlmostEqual(obj.n2_round, round(obj.n2))
+
+    def test_float(self):
+        FloatModel.objects.create(f1=-27.55, f2=0.55)
+        obj = FloatModel.objects.annotate(f1_round=Round('f1'), f2_round=Round('f2')).first()
+        self.assertIsInstance(obj.f1_round, float)
+        self.assertIsInstance(obj.f2_round, float)
+        self.assertAlmostEqual(obj.f1_round, round(obj.f1))
+        self.assertAlmostEqual(obj.f2_round, round(obj.f2))
+
+    def test_integer(self):
+        IntegerModel.objects.create(small=-20, normal=15, big=-1)
+        obj = IntegerModel.objects.annotate(
+            small_round=Round('small'),
+            normal_round=Round('normal'),
+            big_round=Round('big'),
+        ).first()
+        self.assertIsInstance(obj.small_round, int)
+        self.assertIsInstance(obj.normal_round, int)
+        self.assertIsInstance(obj.big_round, int)
+        self.assertEqual(obj.small_round, round(obj.small))
+        self.assertEqual(obj.normal_round, round(obj.normal))
+        self.assertEqual(obj.big_round, round(obj.big))
+
+    def test_transform(self):
+        try:
+            DecimalField.register_lookup(Round)
+            DecimalModel.objects.create(n1=Decimal('2.0'), n2=Decimal('0'))
+            DecimalModel.objects.create(n1=Decimal('-1.0'), n2=Decimal('0'))
+            objs = DecimalModel.objects.filter(n1__round__gt=0)
+            self.assertQuerysetEqual(objs, [Decimal('2.0')], lambda a: a.n1)
+        finally:
+            DecimalField._unregister_lookup(Round)