django: fix 'week' lookup (#380)

* django: fix 'week' lookup.

Translates lookup type `week` into `isoweek`,
when used in either of:
* DatabaseOperations.date_extract_sql
* DatabaseOperations.datetime_extract_sql

in order to conform to Django's ISO 8601 week expectations.

The generated SQL will thus be:

    SELECT EXTRACT(isoweek from DATE(dt.start_time) from db_functions

intead of

    SELECT EXTRACT(week from DATE(dt.start_time) from db_functions

Fixes #263

Author: odeke-em

packages/django-google-spanner/django_spanner/features.py

@@ -116,15 +116,6 @@ class DatabaseFeatures(BaseDatabaseFeatures):
         'timezones.tests.NewDatabaseTests.test_query_datetimes',
         # To be investigated: https://github.com/orijtech/spanner-orm/issues/135
         'admin_changelist.tests.ChangeListTests.test_multiuser_edit',
-        # Spanner's EXTRACT() 'week' differs from Django:
-        # https://github.com/orijtech/spanner-orm/issues/263
-        'db_functions.datetime.test_extract_trunc.DateFunctionTests.test_extract_func',
-        'db_functions.datetime.test_extract_trunc.DateFunctionTests.test_extract_week_func',
-        'db_functions.datetime.test_extract_trunc.DateFunctionTests.test_extract_week_func_boundaries',
-        'db_functions.datetime.test_extract_trunc.DateFunctionWithTimeZoneTests.test_extract_func',
-        'db_functions.datetime.test_extract_trunc.DateFunctionWithTimeZoneTests.test_extract_func_with_timezone',
-        'db_functions.datetime.test_extract_trunc.DateFunctionWithTimeZoneTests.test_extract_week_func',
-        'db_functions.datetime.test_extract_trunc.DateFunctionWithTimeZoneTests.test_extract_week_func_boundaries',
         # using NULL with + crashes: https://github.com/orijtech/spanner-orm/issues/201
         'annotations.tests.NonAggregateAnnotationTestCase.test_combined_annotation_commutative',
         # Spanner loses DecimalField precision due to conversion to float:

packages/django-google-spanner/django_spanner/operations.py

@@ -30,9 +30,9 @@ class DatabaseOperations(BaseDatabaseOperations):
     # EXTRACT() function.
     # https://cloud.google.com/spanner/docs/functions-and-operators#extract
     extract_names = {
-        'week_day': 'dayofweek',
-        'iso_week': 'isoweek',
         'iso_year': 'isoyear',
+        'week': 'isoweek',
+        'week_day': 'dayofweek',
     }
 
     def max_name_length(self):