Refs #14030 -- Improved expression support for python values

django/db/backends/base/features.py

@@ -1,5 +1,4 @@
 from django.db.models.aggregates import StdDev
-from django.db.models.expressions import Value
 from django.db.utils import ProgrammingError
 from django.utils.functional import cached_property
 
@@ -232,7 +231,7 @@ class BaseDatabaseFeatures(object):
     def supports_stddev(self):
         """Confirm support for STDDEV and related stats functions."""
         try:
-            self.connection.ops.check_expression_support(StdDev(Value(1)))
+            self.connection.ops.check_expression_support(StdDev(1))
             return True
         except NotImplementedError:
             return False

django/db/models/expressions.py

@@ -7,7 +7,7 @@ from django.db.backends import utils as backend_utils
 from django.db.models import fields
 from django.db.models.constants import LOOKUP_SEP
 from django.db.models.query_utils import Q, refs_aggregate
-from django.utils import timezone
+from django.utils import six, timezone
 from django.utils.functional import cached_property
 
 
@@ -138,6 +138,13 @@ class BaseExpression(object):
     def set_source_expressions(self, exprs):
         assert len(exprs) == 0
 
+    def _parse_expressions(self, *expressions):
+        return [
+            arg if hasattr(arg, 'resolve_expression') else (
+                F(arg) if isinstance(arg, six.string_types) else Value(arg)
+            ) for arg in expressions
+        ]
+
     def as_sql(self, compiler, connection):
         """
         Responsible for returning a (sql, [params]) tuple to be included
@@ -466,12 +473,6 @@ class Func(ExpressionNode):
     def set_source_expressions(self, exprs):
         self.source_expressions = exprs
 
-    def _parse_expressions(self, *expressions):
-        return [
-            arg if hasattr(arg, 'resolve_expression') else F(arg)
-            for arg in expressions
-        ]
-
     def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
         c = self.copy()
         c.is_summary = summarize
@@ -639,14 +640,14 @@ class Ref(ExpressionNode):
 class When(ExpressionNode):
     template = 'WHEN %(condition)s THEN %(result)s'
 
-    def __init__(self, condition=None, then=Value(None), **lookups):
+    def __init__(self, condition=None, then=None, **lookups):
         if lookups and condition is None:
             condition, lookups = Q(**lookups), None
         if condition is None or not isinstance(condition, Q) or lookups:
             raise TypeError("__init__() takes either a Q object or lookups as keyword arguments")
         super(When, self).__init__(output_field=None)
         self.condition = condition
-        self.result = self._parse_expression(then)
+        self.result = self._parse_expressions(then)[0]
 
     def __str__(self):
         return "WHEN %r THEN %r" % (self.condition, self.result)
@@ -664,9 +665,6 @@ class When(ExpressionNode):
         # We're only interested in the fields of the result expressions.
         return [self.result._output_field_or_none]
 
-    def _parse_expression(self, expression):
-        return expression if hasattr(expression, 'resolve_expression') else F(expression)
-
     def resolve_expression(self, query=None, allow_joins=True, reuse=None, summarize=False, for_save=False):
         c = self.copy()
         c.is_summary = summarize
@@ -713,11 +711,11 @@ class Case(ExpressionNode):
     def __init__(self, *cases, **extra):
         if not all(isinstance(case, When) for case in cases):
             raise TypeError("Positional arguments must all be When objects.")
-        default = extra.pop('default', Value(None))
+        default = extra.pop('default', None)
         output_field = extra.pop('output_field', None)
         super(Case, self).__init__(output_field)
         self.cases = list(cases)
-        self.default = default if hasattr(default, 'resolve_expression') else F(default)
+        self.default = self._parse_expressions(default)[0]
 
     def __str__(self):
         return "CASE %s, ELSE %r" % (', '.join(str(c) for c in self.cases), self.default)

docs/ref/models/conditional-expressions.txt

@@ -39,7 +39,7 @@ We'll be using the following model in the subsequent examples::
 When
 ----
 
-.. class:: When(condition=None, then=Value(None), **lookups)
+.. class:: When(condition=None, then=None, **lookups)
 
 A ``When()`` object is used to encapsulate a condition and its result for use
 in the conditional expression. Using a ``When()`` object is similar to using
@@ -73,8 +73,8 @@ Keep in mind that each of these values can be an expression.
     resolved in two ways::
 
         >>> from django.db.models import Value
-        >>> When(then__exact=0, then=Value(1))
-        >>> When(Q(then=0), then=Value(1))
+        >>> When(then__exact=0, then=1)
+        >>> When(Q(then=0), then=1)
 
 Case
 ----
@@ -197,15 +197,15 @@ What if we want to find out how many clients there are for each
     >>> from django.db.models import IntegerField, Sum
     >>> Client.objects.aggregate(
     ...     regular=Sum(
-    ...         Case(When(account_type=Client.REGULAR, then=Value(1)),
+    ...         Case(When(account_type=Client.REGULAR, then=1),
     ...              output_field=IntegerField())
     ...     ),
     ...     gold=Sum(
-    ...         Case(When(account_type=Client.GOLD, then=Value(1)),
+    ...         Case(When(account_type=Client.GOLD, then=1),
     ...              output_field=IntegerField())
     ...     ),
     ...     platinum=Sum(
-    ...         Case(When(account_type=Client.PLATINUM, then=Value(1)),
+    ...         Case(When(account_type=Client.PLATINUM, then=1),
     ...              output_field=IntegerField())
     ...     )
     ... )

docs/ref/models/expressions.txt

@@ -217,6 +217,10 @@ function will be applied to. The expressions will be converted to strings,
 joined together with ``arg_joiner``, and then interpolated into the ``template``
 as the ``expressions`` placeholder.
 
+Positional arguments can be expressions or Python values. Strings are
+assumed to be column references and will be wrapped in ``F()`` expressions
+while other values will be wrapped in ``Value()`` expressions.
+
 The ``**extra`` kwargs are ``key=value`` pairs that can be interpolated
 into the ``template`` attribute. Note that the keywords ``function`` and
 ``template`` can be used to replace the ``function`` and ``template``

tests/aggregation/tests.py

@@ -8,7 +8,7 @@ from django.core.exceptions import FieldError
 from django.db import connection
 from django.db.models import (
     F, Aggregate, Avg, Count, DecimalField, FloatField, Func, IntegerField,
-    Max, Min, Sum, Value,
+    Max, Min, Sum,
 )
 from django.test import TestCase, ignore_warnings
 from django.test.utils import Approximate, CaptureQueriesContext
@@ -706,14 +706,14 @@ class ComplexAggregateTestCase(TestCase):
             Book.objects.aggregate(fail=F('price'))
 
     def test_nonfield_annotation(self):
-        book = Book.objects.annotate(val=Max(Value(2, output_field=IntegerField())))[0]
+        book = Book.objects.annotate(val=Max(2, output_field=IntegerField()))[0]
         self.assertEqual(book.val, 2)
-        book = Book.objects.annotate(val=Max(Value(2), output_field=IntegerField()))[0]
+        book = Book.objects.annotate(val=Max(2, output_field=IntegerField()))[0]
         self.assertEqual(book.val, 2)
 
     def test_missing_output_field_raises_error(self):
         with six.assertRaisesRegex(self, FieldError, 'Cannot resolve expression type, unknown output_field'):
-            Book.objects.annotate(val=Max(Value(2)))[0]
+            Book.objects.annotate(val=Max(2))[0]
 
     def test_annotation_expressions(self):
         authors = Author.objects.annotate(combined_ages=Sum(F('age') + F('friends__age'))).order_by('name')
@@ -772,7 +772,7 @@ class ComplexAggregateTestCase(TestCase):
         with six.assertRaisesRegex(self, TypeError, 'Complex aggregates require an alias'):
             Author.objects.aggregate(Sum('age') / Count('age'))
         with six.assertRaisesRegex(self, TypeError, 'Complex aggregates require an alias'):
-            Author.objects.aggregate(Sum(Value(1)))
+            Author.objects.aggregate(Sum(1))
 
     def test_aggregate_over_complex_annotation(self):
         qs = Author.objects.annotate(

tests/db_functions/tests.py

@@ -281,7 +281,7 @@ class FunctionTests(TestCase):
     def test_substr_with_expressions(self):
         Author.objects.create(name='John Smith', alias='smithj')
         Author.objects.create(name='Rhonda')
-        authors = Author.objects.annotate(name_part=Substr('name', V(5), V(3)))
+        authors = Author.objects.annotate(name_part=Substr('name', 5, 3))
         self.assertQuerysetEqual(
             authors.order_by('name'), [
                 ' Sm',

tests/expressions_case/tests.py

@@ -78,8 +78,8 @@ class CaseExpressionTests(TestCase):
     def test_annotate_without_default(self):
         self.assertQuerysetEqual(
             CaseTestModel.objects.annotate(test=Case(
-                When(integer=1, then=Value(1)),
-                When(integer=2, then=Value(2)),
+                When(integer=1, then=1),
+                When(integer=2, then=2),
                 output_field=models.IntegerField(),
             )).order_by('pk'),
             [(1, 1), (2, 2), (3, None), (2, 2), (3, None), (3, None), (4, None)],
@@ -244,9 +244,9 @@ class CaseExpressionTests(TestCase):
         self.assertQuerysetEqual(
             CaseTestModel.objects.annotate(
                 test=Case(
-                    When(integer=1, then=Value(2)),
-                    When(integer=2, then=Value(1)),
-                    default=Value(3),
+                    When(integer=1, then=2),
+                    When(integer=2, then=1),
+                    default=3,
                     output_field=models.IntegerField(),
                 ) + 1,
             ).order_by('pk'),
@@ -278,19 +278,19 @@ class CaseExpressionTests(TestCase):
         self.assertEqual(
             CaseTestModel.objects.aggregate(
                 one=models.Sum(Case(
-                    When(integer=1, then=Value(1)),
+                    When(integer=1, then=1),
                     output_field=models.IntegerField(),
                 )),
                 two=models.Sum(Case(
-                    When(integer=2, then=Value(1)),
+                    When(integer=2, then=1),
                     output_field=models.IntegerField(),
                 )),
                 three=models.Sum(Case(
-                    When(integer=3, then=Value(1)),
+                    When(integer=3, then=1),
                     output_field=models.IntegerField(),
                 )),
                 four=models.Sum(Case(
-                    When(integer=4, then=Value(1)),
+                    When(integer=4, then=1),
                     output_field=models.IntegerField(),
                 )),
             ),
@@ -311,11 +311,11 @@ class CaseExpressionTests(TestCase):
         self.assertEqual(
             CaseTestModel.objects.aggregate(
                 equal=models.Sum(Case(
-                    When(integer2=F('integer'), then=Value(1)),
+                    When(integer2=F('integer'), then=1),
                     output_field=models.IntegerField(),
                 )),
                 plus_one=models.Sum(Case(
-                    When(integer2=F('integer') + 1, then=Value(1)),
+                    When(integer2=F('integer') + 1, then=1),
                     output_field=models.IntegerField(),
                 )),
             ),
@@ -325,9 +325,9 @@ class CaseExpressionTests(TestCase):
     def test_filter(self):
         self.assertQuerysetEqual(
             CaseTestModel.objects.filter(integer2=Case(
-                When(integer=2, then=Value(3)),
-                When(integer=3, then=Value(4)),
-                default=Value(1),
+                When(integer=2, then=3),
+                When(integer=3, then=4),
+                default=1,
                 output_field=models.IntegerField(),
             )).order_by('pk'),
             [(1, 1), (2, 3), (3, 4), (3, 4)],
@@ -337,8 +337,8 @@ class CaseExpressionTests(TestCase):
     def test_filter_without_default(self):
         self.assertQuerysetEqual(
             CaseTestModel.objects.filter(integer2=Case(
-                When(integer=2, then=Value(3)),
-                When(integer=3, then=Value(4)),
+                When(integer=2, then=3),
+                When(integer=3, then=4),
                 output_field=models.IntegerField(),
             )).order_by('pk'),
             [(2, 3), (3, 4), (3, 4)],
@@ -381,8 +381,8 @@ class CaseExpressionTests(TestCase):
     def test_filter_with_join_in_condition(self):
         self.assertQuerysetEqual(
             CaseTestModel.objects.filter(integer=Case(
-                When(integer2=F('o2o_rel__integer') + 1, then=Value(2)),
-                When(integer2=F('o2o_rel__integer'), then=Value(3)),
+                When(integer2=F('o2o_rel__integer') + 1, then=2),
+                When(integer2=F('o2o_rel__integer'), then=3),
                 output_field=models.IntegerField(),
             )).order_by('pk'),
             [(2, 3), (3, 3)],
@@ -392,9 +392,9 @@ class CaseExpressionTests(TestCase):
     def test_filter_with_join_in_predicate(self):
         self.assertQuerysetEqual(
             CaseTestModel.objects.filter(integer2=Case(
-                When(o2o_rel__integer=1, then=Value(1)),
-                When(o2o_rel__integer=2, then=Value(3)),
-                When(o2o_rel__integer=3, then=Value(4)),
+                When(o2o_rel__integer=1, then=1),
+                When(o2o_rel__integer=2, then=3),
+                When(o2o_rel__integer=3, then=4),
                 output_field=models.IntegerField(),
             )).order_by('pk'),
             [(1, 1), (2, 3), (3, 4), (3, 4)],
@@ -422,8 +422,8 @@ class CaseExpressionTests(TestCase):
                 f_plus_1=F('integer') + 1,
             ).filter(
                 integer=Case(
-                    When(integer2=F('integer'), then=Value(2)),
-                    When(integer2=F('f_plus_1'), then=Value(3)),
+                    When(integer2=F('integer'), then=2),
+                    When(integer2=F('f_plus_1'), then=3),
                     output_field=models.IntegerField(),
                 ),
             ).order_by('pk'),
@@ -437,9 +437,9 @@ class CaseExpressionTests(TestCase):
                 f_plus_1=F('integer') + 1,
             ).filter(
                 integer2=Case(
-                    When(f_plus_1=3, then=Value(3)),
-                    When(f_plus_1=4, then=Value(4)),
-                    default=Value(1),
+                    When(f_plus_1=3, then=3),
+                    When(f_plus_1=4, then=4),
+                    default=1,
                     output_field=models.IntegerField(),
                 ),
             ).order_by('pk'),
@@ -469,8 +469,8 @@ class CaseExpressionTests(TestCase):
                 max=Max('fk_rel__integer'),
             ).filter(
                 integer=Case(
-                    When(integer2=F('min'), then=Value(2)),
-                    When(integer2=F('max'), then=Value(3)),
+                    When(integer2=F('min'), then=2),
+                    When(integer2=F('max'), then=3),
                 ),
             ).order_by('pk'),
             [(3, 4, 3, 4), (2, 2, 2, 3), (3, 4, 3, 4)],
@@ -483,8 +483,8 @@ class CaseExpressionTests(TestCase):
                 max=Max('fk_rel__integer'),
             ).filter(
                 integer=Case(
-                    When(max=3, then=Value(2)),
-                    When(max=4, then=Value(3)),
+                    When(max=3, then=2),
+                    When(max=4, then=3),
                 ),
             ).order_by('pk'),
             [(2, 3, 3), (3, 4, 4), (2, 2, 3), (3, 4, 4), (3, 3, 4)],
@@ -508,8 +508,8 @@ class CaseExpressionTests(TestCase):
     def test_update_without_default(self):
         CaseTestModel.objects.update(
             integer2=Case(
-                When(integer=1, then=Value(1)),
-                When(integer=2, then=Value(2)),
+                When(integer=1, then=1),
+                When(integer=2, then=2),
             ),
         )
         self.assertQuerysetEqual(
@@ -549,8 +549,8 @@ class CaseExpressionTests(TestCase):
         with self.assertRaisesMessage(FieldError, 'Joined field references are not permitted in this query'):
             CaseTestModel.objects.update(
                 integer=Case(
-                    When(integer2=F('o2o_rel__integer') + 1, then=Value(2)),
-                    When(integer2=F('o2o_rel__integer'), then=Value(3)),
+                    When(integer2=F('o2o_rel__integer') + 1, then=2),
+                    When(integer2=F('o2o_rel__integer'), then=3),
                     output_field=models.IntegerField(),
                 ),
             )
@@ -570,8 +570,8 @@ class CaseExpressionTests(TestCase):
     def test_update_big_integer(self):
         CaseTestModel.objects.update(
             big_integer=Case(
-                When(integer=1, then=Value(1)),
-                When(integer=2, then=Value(2)),
+                When(integer=1, then=1),
+                When(integer=2, then=2),
             ),
         )
         self.assertQuerysetEqual(
@@ -599,9 +599,9 @@ class CaseExpressionTests(TestCase):
     def test_update_boolean(self):
         CaseTestModel.objects.update(
             boolean=Case(
-                When(integer=1, then=Value(True)),
-                When(integer=2, then=Value(True)),
-                default=Value(False),
+                When(integer=1, then=True),
+                When(integer=2, then=True),
+                default=False,
             ),
         )
         self.assertQuerysetEqual(
@@ -627,8 +627,8 @@ class CaseExpressionTests(TestCase):
     def test_update_date(self):
         CaseTestModel.objects.update(
             date=Case(
-                When(integer=1, then=Value(date(2015, 1, 1))),
-                When(integer=2, then=Value(date(2015, 1, 2))),
+                When(integer=1, then=date(2015, 1, 1)),
+                When(integer=2, then=date(2015, 1, 2)),
             ),
         )
         self.assertQuerysetEqual(
@@ -643,8 +643,8 @@ class CaseExpressionTests(TestCase):
     def test_update_date_time(self):
         CaseTestModel.objects.update(
             date_time=Case(
-                When(integer=1, then=Value(datetime(2015, 1, 1))),
-                When(integer=2, then=Value(datetime(2015, 1, 2))),
+                When(integer=1, then=datetime(2015, 1, 1)),
+                When(integer=2, then=datetime(2015, 1, 2)),
             ),
         )
         self.assertQuerysetEqual(
@@ -659,8 +659,8 @@ class CaseExpressionTests(TestCase):
     def test_update_decimal(self):
         CaseTestModel.objects.update(
             decimal=Case(
-                When(integer=1, then=Value(Decimal('1.1'))),
-                When(integer=2, then=Value(Decimal('2.2'))),
+                When(integer=1, then=Decimal('1.1')),
+                When(integer=2, then=Decimal('2.2')),
             ),
         )
         self.assertQuerysetEqual(
@@ -728,8 +728,8 @@ class CaseExpressionTests(TestCase):
     def test_update_float(self):
         CaseTestModel.objects.update(
             float=Case(
-                When(integer=1, then=Value(1.1)),
-                When(integer=2, then=Value(2.2)),
+                When(integer=1, then=1.1),
+                When(integer=2, then=2.2),
             ),
         )
         self.assertQuerysetEqual(
@@ -770,8 +770,8 @@ class CaseExpressionTests(TestCase):
     def test_update_null_boolean(self):
         CaseTestModel.objects.update(
             null_boolean=Case(
-                When(integer=1, then=Value(True)),
-                When(integer=2, then=Value(False)),
+                When(integer=1, then=True),
+                When(integer=2, then=False),
             ),
         )
         self.assertQuerysetEqual(
@@ -783,8 +783,8 @@ class CaseExpressionTests(TestCase):
     def test_update_positive_integer(self):
         CaseTestModel.objects.update(
             positive_integer=Case(
-                When(integer=1, then=Value(1)),
-                When(integer=2, then=Value(2)),
+                When(integer=1, then=1),
+                When(integer=2, then=2),
             ),
         )
         self.assertQuerysetEqual(
@@ -796,8 +796,8 @@ class CaseExpressionTests(TestCase):
     def test_update_positive_small_integer(self):
         CaseTestModel.objects.update(
             positive_small_integer=Case(
-                When(integer=1, then=Value(1)),
-                When(integer=2, then=Value(2)),
+                When(integer=1, then=1),
+                When(integer=2, then=2),
             ),
         )
         self.assertQuerysetEqual(
@@ -823,8 +823,8 @@ class CaseExpressionTests(TestCase):
     def test_update_small_integer(self):
         CaseTestModel.objects.update(
             small_integer=Case(
-                When(integer=1, then=Value(1)),
-                When(integer=2, then=Value(2)),
+                When(integer=1, then=1),
+                When(integer=2, then=2),
             ),
         )
         self.assertQuerysetEqual(
@@ -921,8 +921,8 @@ class CaseExpressionTests(TestCase):
 
         CaseTestModel.objects.update(
             fk=Case(
-                When(integer=1, then=Value(obj1.pk)),
-                When(integer=2, then=Value(obj2.pk)),
+                When(integer=1, then=obj1.pk),
+                When(integer=2, then=obj2.pk),
             ),
         )
         self.assertQuerysetEqual(
@@ -1065,15 +1065,15 @@ class CaseDocumentationExamples(TestCase):
         self.assertEqual(
             Client.objects.aggregate(
                 regular=models.Sum(Case(
-                    When(account_type=Client.REGULAR, then=Value(1)),
+                    When(account_type=Client.REGULAR, then=1),
                     output_field=models.IntegerField(),
                 )),
                 gold=models.Sum(Case(
-                    When(account_type=Client.GOLD, then=Value(1)),
+                    When(account_type=Client.GOLD, then=1),
                     output_field=models.IntegerField(),
                 )),
                 platinum=models.Sum(Case(
-                    When(account_type=Client.PLATINUM, then=Value(1)),
+                    When(account_type=Client.PLATINUM, then=1),
                     output_field=models.IntegerField(),
                 )),
             ),