Fixed #30271 -- Added the Sign database function.

django/db/backends/sqlite3/base.py

@@ -231,6 +231,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         conn.create_function('SHA256', 1, none_guard(lambda x: hashlib.sha256(x.encode()).hexdigest()))
         conn.create_function('SHA384', 1, none_guard(lambda x: hashlib.sha384(x.encode()).hexdigest()))
         conn.create_function('SHA512', 1, none_guard(lambda x: hashlib.sha512(x.encode()).hexdigest()))
+        conn.create_function('SIGN', 1, none_guard(lambda x: (x > 0) - (x < 0)))
         conn.create_function('SIN', 1, none_guard(math.sin))
         conn.create_function('SQRT', 1, none_guard(math.sqrt))
         conn.create_function('TAN', 1, none_guard(math.tan))

django/db/models/functions/__init__.py

@@ -7,7 +7,7 @@ from .datetime import (
 )
 from .math import (
     Abs, ACos, ASin, ATan, ATan2, Ceil, Cos, Cot, Degrees, Exp, Floor, Ln, Log,
-    Mod, Pi, Power, Radians, Round, Sin, Sqrt, Tan,
+    Mod, Pi, Power, Radians, Round, Sign, Sin, Sqrt, Tan,
 )
 from .text import (
     MD5, SHA1, SHA224, SHA256, SHA384, SHA512, Chr, Concat, ConcatPair, Left,
@@ -32,7 +32,7 @@ __all__ = [
     # math
     'Abs', 'ACos', 'ASin', 'ATan', 'ATan2', 'Ceil', 'Cos', 'Cot', 'Degrees',
     'Exp', 'Floor', 'Ln', 'Log', 'Mod', 'Pi', 'Power', 'Radians', 'Round',
-    'Sin', 'Sqrt', 'Tan',
+    'Sign', 'Sin', 'Sqrt', 'Tan',
     # text
     'MD5', 'SHA1', 'SHA224', 'SHA256', 'SHA384', 'SHA512', 'Chr', 'Concat',
     'ConcatPair', 'Left', 'Length', 'Lower', 'LPad', 'LTrim', 'Ord', 'Repeat',

django/db/models/functions/math.py

@@ -146,6 +146,11 @@ class Round(Transform):
     lookup_name = 'round'
 
 
+class Sign(Transform):
+    function = 'SIGN'
+    lookup_name = 'sign'
+
+
 class Sin(NumericOutputFieldMixin, Transform):
     function = 'SIN'
     lookup_name = 'sin'

docs/ref/models/database-functions.txt

@@ -1099,6 +1099,31 @@ It can also be registered as a transform. For example::
     >>> # Get vectors whose round() is less than 20
     >>> vectors = Vector.objects.filter(x__round__lt=20, y__round__lt=20)
 
+``Sign``
+--------
+
+.. class:: Sign(expression, **extra)
+
+.. versionadded:: 3.0
+
+Returns the sign (-1, 0, 1) of a numeric field or expression.
+
+Usage example::
+
+    >>> from django.db.models.functions import Sign
+    >>> Vector.objects.create(x=5.4, y=-2.3)
+    >>> vector = Vector.objects.annotate(x_sign=Sign('x'), y_sign=Sign('y')).get()
+    >>> vector.x_sign, vector.y_sign
+    (1, -1)
+
+It can also be registered as a transform. For example::
+
+    >>> from django.db.models import FloatField
+    >>> from django.db.models.functions import Sign
+    >>> FloatField.register_lookup(Sign)
+    >>> # Get vectors whose signs of components are less than 0.
+    >>> vectors = Vector.objects.filter(x__sign__lt=0, y__sign__lt=0)
+
 ``Sin``
 -------
 

docs/releases/3.0.txt

@@ -178,6 +178,8 @@ Models
   :class:`~django.db.models.functions.SHA384`, and
   :class:`~django.db.models.functions.SHA512`.
 
+* Added the :class:`~django.db.models.functions.Sign` database function.
+
 * The new ``is_dst``  parameter of the
   :class:`~django.db.models.functions.Trunc` database functions determines the
   treatment of nonexistent and ambiguous datetimes.

tests/db_functions/math/test_sign.py

@@ -0,0 +1,53 @@
+from decimal import Decimal
+
+from django.db.models import DecimalField
+from django.db.models.functions import Sign
+from django.test import TestCase
+from django.test.utils import register_lookup
+
+from ..models import DecimalModel, FloatModel, IntegerModel
+
+
+class SignTests(TestCase):
+
+    def test_null(self):
+        IntegerModel.objects.create()
+        obj = IntegerModel.objects.annotate(null_sign=Sign('normal')).first()
+        self.assertIsNone(obj.null_sign)
+
+    def test_decimal(self):
+        DecimalModel.objects.create(n1=Decimal('-12.9'), n2=Decimal('0.6'))
+        obj = DecimalModel.objects.annotate(n1_sign=Sign('n1'), n2_sign=Sign('n2')).first()
+        self.assertIsInstance(obj.n1_sign, Decimal)
+        self.assertIsInstance(obj.n2_sign, Decimal)
+        self.assertEqual(obj.n1_sign, Decimal('-1'))
+        self.assertEqual(obj.n2_sign, Decimal('1'))
+
+    def test_float(self):
+        FloatModel.objects.create(f1=-27.5, f2=0.33)
+        obj = FloatModel.objects.annotate(f1_sign=Sign('f1'), f2_sign=Sign('f2')).first()
+        self.assertIsInstance(obj.f1_sign, float)
+        self.assertIsInstance(obj.f2_sign, float)
+        self.assertEqual(obj.f1_sign, -1.0)
+        self.assertEqual(obj.f2_sign, 1.0)
+
+    def test_integer(self):
+        IntegerModel.objects.create(small=-20, normal=0, big=20)
+        obj = IntegerModel.objects.annotate(
+            small_sign=Sign('small'),
+            normal_sign=Sign('normal'),
+            big_sign=Sign('big'),
+        ).first()
+        self.assertIsInstance(obj.small_sign, int)
+        self.assertIsInstance(obj.normal_sign, int)
+        self.assertIsInstance(obj.big_sign, int)
+        self.assertEqual(obj.small_sign, -1)
+        self.assertEqual(obj.normal_sign, 0)
+        self.assertEqual(obj.big_sign, 1)
+
+    def test_transform(self):
+        with register_lookup(DecimalField, Sign):
+            DecimalModel.objects.create(n1=Decimal('5.4'), n2=Decimal('0'))
+            DecimalModel.objects.create(n1=Decimal('-0.1'), n2=Decimal('0'))
+            obj = DecimalModel.objects.filter(n1__sign__lt=0, n2__sign=0).get()
+            self.assertEqual(obj.n1, Decimal('-0.1'))