Refs #25287 -- Added support for multiplying and dividing DurationField by scalar values on SQLite.

django/db/backends/mysql/features.py

@@ -68,6 +68,10 @@ class DatabaseFeatures(BaseDatabaseFeatures):
             "returns JSON": {
                 'schema.tests.SchemaTests.test_func_index_json_key_transform',
             },
+            "MySQL supports multiplying and dividing DurationFields by a "
+            "scalar value but it's not implemented (#25287).": {
+                'expressions.tests.FTimeDeltaTests.test_durationfield_multiply_divide',
+            },
         }
         if 'ONLY_FULL_GROUP_BY' in self.connection.sql_mode:
             skips.update({

django/db/backends/sqlite3/base.py

@@ -563,6 +563,7 @@ def _sqlite_format_dtdelta(conn, lhs, rhs):
     LHS and RHS can be either:
     - An integer number of microseconds
     - A string representing a datetime
+    - A scalar value, e.g. float
     """
     conn = conn.strip()
     try:
@@ -574,8 +575,12 @@ def _sqlite_format_dtdelta(conn, lhs, rhs):
         # typecast_timestamp returns a date or a datetime without timezone.
         # It will be formatted as "%Y-%m-%d" or "%Y-%m-%d %H:%M:%S[.%f]"
         out = str(real_lhs + real_rhs)
-    else:
+    elif conn == '-':
         out = str(real_lhs - real_rhs)
+    elif conn == '*':
+        out = real_lhs * real_rhs
+    else:
+        out = real_lhs / real_rhs
     return out
 
 

django/db/backends/sqlite3/operations.py

@@ -351,7 +351,7 @@ class DatabaseOperations(BaseDatabaseOperations):
         return super().combine_expression(connector, sub_expressions)
 
     def combine_duration_expression(self, connector, sub_expressions):
-        if connector not in ['+', '-']:
+        if connector not in ['+', '-', '*', '/']:
             raise DatabaseError('Invalid connector for timedelta: %s.' % connector)
         fn_params = ["'%s'" % connector] + sub_expressions
         if len(fn_params) > 3:

django/db/models/expressions.py

@@ -6,7 +6,7 @@ from decimal import Decimal
 from uuid import UUID
 
 from django.core.exceptions import EmptyResultSet, FieldError
-from django.db import NotSupportedError, connection
+from django.db import DatabaseError, NotSupportedError, connection
 from django.db.models import fields
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.query_utils import Q
@@ -546,6 +546,24 @@ class DurationExpression(CombinedExpression):
         sql = connection.ops.combine_duration_expression(self.connector, expressions)
         return expression_wrapper % sql, expression_params
 
+    def as_sqlite(self, compiler, connection, **extra_context):
+        sql, params = self.as_sql(compiler, connection, **extra_context)
+        if self.connector in {Combinable.MUL, Combinable.DIV}:
+            try:
+                lhs_type = self.lhs.output_field.get_internal_type()
+                rhs_type = self.rhs.output_field.get_internal_type()
+            except (AttributeError, FieldError):
+                pass
+            else:
+                allowed_fields = {
+                    'DecimalField', 'DurationField', 'FloatField', 'IntegerField',
+                }
+                if lhs_type not in allowed_fields or rhs_type not in allowed_fields:
+                    raise DatabaseError(
+                        f'Invalid arguments for operator {self.connector}.'
+                    )
+        return sql, params
+
 
 class TemporalSubtraction(CombinedExpression):
     output_field = fields.DurationField()

docs/releases/4.0.txt

@@ -233,6 +233,9 @@ Models
 * :meth:`.QuerySet.bulk_create` now sets the primary key on objects when using
   SQLite 3.35+.
 
+* :class:`~django.db.models.DurationField` now supports multiplying and
+  dividing by scalar values on SQLite.
+
 Requests and Responses
 ~~~~~~~~~~~~~~~~~~~~~~
 

tests/expressions/models.py

@@ -60,6 +60,7 @@ class Experiment(models.Model):
     estimated_time = models.DurationField()
     start = models.DateTimeField()
     end = models.DateTimeField()
+    scalar = models.IntegerField(null=True)
 
     class Meta:
         db_table = 'expressions_ExPeRiMeNt'

tests/expressions/tests.py

@@ -1530,6 +1530,36 @@ class FTimeDeltaTests(TestCase):
         ))
         self.assertIsNone(queryset.first().shifted)
 
+    def test_durationfield_multiply_divide(self):
+        Experiment.objects.update(scalar=2)
+        tests = [
+            (Decimal('2'), 2),
+            (F('scalar'), 2),
+            (2, 2),
+            (3.2, 3.2),
+        ]
+        for expr, scalar in tests:
+            with self.subTest(expr=expr):
+                qs = Experiment.objects.annotate(
+                    multiplied=ExpressionWrapper(
+                        expr * F('estimated_time'),
+                        output_field=DurationField(),
+                    ),
+                    divided=ExpressionWrapper(
+                        F('estimated_time') / expr,
+                        output_field=DurationField(),
+                    ),
+                )
+                for experiment in qs:
+                    self.assertEqual(
+                        experiment.multiplied,
+                        experiment.estimated_time * scalar,
+                    )
+                    self.assertEqual(
+                        experiment.divided,
+                        experiment.estimated_time / scalar,
+                    )
+
     def test_duration_expressions(self):
         for delta in self.deltas:
             qs = Experiment.objects.annotate(duration=F('estimated_time') + delta)