Fixed #25240 -- Added ExtractWeek and exposed it through the __week lookup.

Thanks to Mariusz Felisiak and Tim Graham for review.

5 files changed, 26 insertions, 3 deletions

diff --git a/django/db/backends/mysql/operations.py b/django/db/backends/mysql/operations.py
index 306a0378b2..772ae1e37d 100644
--- a/django/db/backends/mysql/operations.py
+++ b/django/db/backends/mysql/operations.py
@@ -24,7 +24,13 @@ class DatabaseOperations(BaseDatabaseOperations):
             # DAYOFWEEK() returns an integer, 1-7, Sunday=1.
             # Note: WEEKDAY() returns 0-6, Monday=0.
             return "DAYOFWEEK(%s)" % field_name
+        elif lookup_type == 'week':
+            # Override the value of default_week_format for consistency with
+            # other database backends.
+            # Mode 3: Monday, 1-53, with 4 or more days this year.
+            return "WEEK(%s, 3)" % field_name
         else:
+            # EXTRACT returns 1-53 based on ISO-8601 for the week number.
             return "EXTRACT(%s FROM %s)" % (lookup_type.upper(), field_name)
 
     def date_trunc_sql(self, lookup_type, field_name):
diff --git a/django/db/backends/oracle/operations.py b/django/db/backends/oracle/operations.py
index 8191f89dd0..82be9c5241 100644
--- a/django/db/backends/oracle/operations.py
+++ b/django/db/backends/oracle/operations.py
@@ -84,6 +84,9 @@ WHEN (new.%(col_name)s IS NULL)
         if lookup_type == 'week_day':
             # TO_CHAR(field, 'D') returns an integer from 1-7, where 1=Sunday.
             return "TO_CHAR(%s, 'D')" % field_name
+        elif lookup_type == 'week':
+            # IW = ISO week number
+            return "TO_CHAR(%s, 'IW')" % field_name
         else:
             # http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions050.htm
             return "EXTRACT(%s FROM %s)" % (lookup_type.upper(), field_name)
diff --git a/django/db/backends/sqlite3/base.py b/django/db/backends/sqlite3/base.py
index 66ad27842b..aee012c7e6 100644
--- a/django/db/backends/sqlite3/base.py
+++ b/django/db/backends/sqlite3/base.py
@@ -344,6 +344,8 @@ def _sqlite_date_extract(lookup_type, dt):
         return None
     if lookup_type == 'week_day':
         return (dt.isoweekday() % 7) + 1
+    elif lookup_type == 'week':
+        return dt.isocalendar()[1]
     else:
         return getattr(dt, lookup_type)
 
@@ -406,6 +408,8 @@ def _sqlite_datetime_extract(lookup_type, dt, tzname):
         return None
     if lookup_type == 'week_day':
         return (dt.isoweekday() % 7) + 1
+    elif lookup_type == 'week':
+        return dt.isocalendar()[1]
     else:
         return getattr(dt, lookup_type)
 
diff --git a/django/db/models/functions/__init__.py b/django/db/models/functions/__init__.py
index dd45d7bb4c..eeafc1dc48 100644
--- a/django/db/models/functions/__init__.py
+++ b/django/db/models/functions/__init__.py
@@ -4,8 +4,9 @@ from .base import (
 )
 from .datetime import (
     Extract, ExtractDay, ExtractHour, ExtractMinute, ExtractMonth,
-    ExtractSecond, ExtractWeekDay, ExtractYear, Trunc, TruncDate, TruncDay,
-    TruncHour, TruncMinute, TruncMonth, TruncSecond, TruncTime, TruncYear,
+    ExtractSecond, ExtractWeek, ExtractWeekDay, ExtractYear, Trunc, TruncDate,
+    TruncDay, TruncHour, TruncMinute, TruncMonth, TruncSecond, TruncTime,
+    TruncYear,
 )
 
 __all__ = [
@@ -14,7 +15,7 @@ __all__ = [
     'Lower', 'Now', 'Substr', 'Upper',
     # datetime
     'Extract', 'ExtractDay', 'ExtractHour', 'ExtractMinute', 'ExtractMonth',
-    'ExtractSecond', 'ExtractWeekDay', 'ExtractYear',
+    'ExtractSecond', 'ExtractWeek', 'ExtractWeekDay', 'ExtractYear',
     'Trunc', 'TruncDate', 'TruncDay', 'TruncHour', 'TruncMinute', 'TruncMonth',
     'TruncSecond', 'TruncTime', 'TruncYear',
 ]
diff --git a/django/db/models/functions/datetime.py b/django/db/models/functions/datetime.py
index 341c53e162..7b137eabef 100644
--- a/django/db/models/functions/datetime.py
+++ b/django/db/models/functions/datetime.py
@@ -87,6 +87,14 @@ class ExtractDay(Extract):
     lookup_name = 'day'
 
 
+class ExtractWeek(Extract):
+    """
+    Return 1-52 or 53, based on ISO-8601, i.e., Monday is the first of the
+    week.
+    """
+    lookup_name = 'week'
+
+
 class ExtractWeekDay(Extract):
     """
     Return Sunday=1 through Saturday=7.
@@ -112,6 +120,7 @@ DateField.register_lookup(ExtractYear)
 DateField.register_lookup(ExtractMonth)
 DateField.register_lookup(ExtractDay)
 DateField.register_lookup(ExtractWeekDay)
+DateField.register_lookup(ExtractWeek)
 
 TimeField.register_lookup(ExtractHour)
 TimeField.register_lookup(ExtractMinute)