Refs #28643 -- Added math database functions.

Thanks Nick Pope for much review.

tests/db_functions/math/test_sqrt.py

@@ -0,0 +1,51 @@
+import math
+from decimal import Decimal
+
+from django.db.models import DecimalField
+from django.db.models.functions import Sqrt
+from django.test import TestCase
+
+from ..models import DecimalModel, FloatModel, IntegerModel
+
+
+class SqrtTests(TestCase):
+
+    def test_decimal(self):
+        DecimalModel.objects.create(n1=Decimal('12.9'), n2=Decimal('0.6'))
+        obj = DecimalModel.objects.annotate(n1_sqrt=Sqrt('n1'), n2_sqrt=Sqrt('n2')).first()
+        self.assertIsInstance(obj.n1_sqrt, Decimal)
+        self.assertIsInstance(obj.n2_sqrt, Decimal)
+        self.assertAlmostEqual(obj.n1_sqrt, Decimal(math.sqrt(obj.n1)))
+        self.assertAlmostEqual(obj.n2_sqrt, Decimal(math.sqrt(obj.n2)))
+
+    def test_float(self):
+        FloatModel.objects.create(f1=27.5, f2=0.33)
+        obj = FloatModel.objects.annotate(f1_sqrt=Sqrt('f1'), f2_sqrt=Sqrt('f2')).first()
+        self.assertIsInstance(obj.f1_sqrt, float)
+        self.assertIsInstance(obj.f2_sqrt, float)
+        self.assertAlmostEqual(obj.f1_sqrt, math.sqrt(obj.f1))
+        self.assertAlmostEqual(obj.f2_sqrt, math.sqrt(obj.f2))
+
+    def test_integer(self):
+        IntegerModel.objects.create(small=20, normal=15, big=1)
+        obj = IntegerModel.objects.annotate(
+            small_sqrt=Sqrt('small'),
+            normal_sqrt=Sqrt('normal'),
+            big_sqrt=Sqrt('big'),
+        ).first()
+        self.assertIsInstance(obj.small_sqrt, float)
+        self.assertIsInstance(obj.normal_sqrt, float)
+        self.assertIsInstance(obj.big_sqrt, float)
+        self.assertAlmostEqual(obj.small_sqrt, math.sqrt(obj.small))
+        self.assertAlmostEqual(obj.normal_sqrt, math.sqrt(obj.normal))
+        self.assertAlmostEqual(obj.big_sqrt, math.sqrt(obj.big))
+
+    def test_transform(self):
+        try:
+            DecimalField.register_lookup(Sqrt)
+            DecimalModel.objects.create(n1=Decimal('6.0'), n2=Decimal('0'))
+            DecimalModel.objects.create(n1=Decimal('1.0'), n2=Decimal('0'))
+            objs = DecimalModel.objects.filter(n1__sqrt__gt=2)
+            self.assertQuerysetEqual(objs, [Decimal('6.0')], lambda a: a.n1)
+        finally:
+            DecimalField._unregister_lookup(Sqrt)