Merge pull request #41 from timnyborg/patch-1

Enable support for window functions

Author: absci

mssql/features.py

@@ -33,6 +33,7 @@ class DatabaseFeatures(BaseDatabaseFeatures):
     supports_index_on_text_field = False
     supports_json_field_contains = False
     supports_order_by_nulls_modifier = False
+    supports_over_clause = True
     supports_paramstyle_pyformat = False
     supports_primitives_in_json_field = False
     supports_regex_backreferencing = True

mssql/functions.py

@@ -4,10 +4,11 @@
 import json
 
 from django import VERSION
-from django.db.models import BooleanField
-from django.db.models.functions import Cast
+from django.db import NotSupportedError
+from django.db.models import BooleanField, Value
+from django.db.models.functions import Cast, NthValue
 from django.db.models.functions.math import ATan2, Log, Ln, Mod, Round
-from django.db.models.expressions import Case, Exists, OrderBy, When
+from django.db.models.expressions import Case, Exists, OrderBy, When, Window
 from django.db.models.lookups import Lookup, In
 from django.db.models import lookups
 
@@ -51,10 +52,21 @@ def sqlserver_mod(self, compiler, connection):
     )
 
 
+def sqlserver_nth_value(self, compiler, connection, **extra_content):
+    raise NotSupportedError('This backend does not support the NthValue function')
+
+
 def sqlserver_round(self, compiler, connection, **extra_context):
     return self.as_sql(compiler, connection, template='%(function)s(%(expressions)s, 0)', **extra_context)
 
 
+def sqlserver_window(self, compiler, connection, template=None):
+    # MSSQL window functions require an OVER clause with ORDER BY
+    if self.order_by is None:
+        self.order_by = Value('SELECT NULL')
+    return self.as_sql(compiler, connection, template)
+
+
 def sqlserver_exists(self, compiler, connection, template=None, **extra_context):
     # MS SQL doesn't allow EXISTS() in the SELECT list, so wrap it with a
     # CASE WHEN expression. Change the template since the When expression
@@ -179,11 +191,14 @@ def json_HasKeyLookup(self, compiler, connection):
 Ln.as_microsoft = sqlserver_ln
 Log.as_microsoft = sqlserver_log
 Mod.as_microsoft = sqlserver_mod
+NthValue.as_microsoft = sqlserver_nth_value
 Round.as_microsoft = sqlserver_round
+Window.as_microsoft = sqlserver_window
 
 if DJANGO3:
     Lookup.as_microsoft = sqlserver_lookup
 else:
     Exists.as_microsoft = sqlserver_exists
 
 OrderBy.as_microsoft = sqlserver_orderby
+

testapp/settings.py

@@ -54,6 +54,9 @@
                   'expressions.tests.FTimeDeltaTests.test_duration_with_datetime_microseconds',
                   'expressions.tests.IterableLookupInnerExpressionsTests.test_expressions_in_lookups_join_choice',
                   'expressions_case.tests.CaseExpressionTests.test_annotate_with_in_clause',
+                  'expressions_window.tests.WindowFunctionTests.test_nth_returns_null',
+                  'expressions_window.tests.WindowFunctionTests.test_nthvalue',
+                  'expressions_window.tests.WindowFunctionTests.test_range_n_preceding_and_following',
                   'ordering.tests.OrderingTests.test_orders_nulls_first_on_filtered_subquery',
                   'queries.test_bulk_update.BulkUpdateNoteTests.test_set_field_to_null',
                   'get_or_create.tests.UpdateOrCreateTransactionTests.test_creation_in_transaction',