Fixed #26348 -- Added TruncTime and exposed it through the __time lookup.

Thanks Tim for the review.

8 files changed, 54 insertions, 2 deletions

diff --git a/django/db/backends/base/operations.py b/django/db/backends/base/operations.py
index 63081ba113..bf9af0149a 100644
--- a/django/db/backends/base/operations.py
+++ b/django/db/backends/base/operations.py
@@ -96,6 +96,12 @@ class BaseDatabaseOperations(object):
         """
         raise NotImplementedError('subclasses of BaseDatabaseOperations may require a datetime_cast_date() method')
 
+    def datetime_cast_time_sql(self, field_name, tzname):
+        """
+        Returns the SQL necessary to cast a datetime value to time value.
+        """
+        raise NotImplementedError('subclasses of BaseDatabaseOperations may require a datetime_cast_time_sql() method')
+
     def datetime_extract_sql(self, lookup_type, field_name, tzname):
         """
         Given a lookup_type of 'year', 'month', 'day', 'hour', 'minute' or
diff --git a/django/db/backends/mysql/operations.py b/django/db/backends/mysql/operations.py
index 5ced46f970..f0fd8314ae 100644
--- a/django/db/backends/mysql/operations.py
+++ b/django/db/backends/mysql/operations.py
@@ -51,6 +51,11 @@ class DatabaseOperations(BaseDatabaseOperations):
         sql = "DATE(%s)" % field_name
         return sql, params
 
+    def datetime_cast_time_sql(self, field_name, tzname):
+        field_name, params = self._convert_field_to_tz(field_name, tzname)
+        sql = "TIME(%s)" % field_name
+        return sql, params
+
     def datetime_extract_sql(self, lookup_type, field_name, tzname):
         field_name, params = self._convert_field_to_tz(field_name, tzname)
         sql = self.date_extract_sql(lookup_type, field_name)
diff --git a/django/db/backends/oracle/operations.py b/django/db/backends/oracle/operations.py
index 0a6a239956..3761ed0df1 100644
--- a/django/db/backends/oracle/operations.py
+++ b/django/db/backends/oracle/operations.py
@@ -128,6 +128,12 @@ WHEN (new.%(col_name)s IS NULL)
         sql = 'TRUNC(%s)' % field_name
         return sql, []
 
+    def datetime_cast_time_sql(self, field_name, tzname):
+        # Since `TimeField` values are stored as TIMESTAMP where only the date
+        # part is ignored, convert the field to the specified timezone.
+        field_name = self._convert_field_to_tz(field_name, tzname)
+        return field_name, []
+
     def datetime_extract_sql(self, lookup_type, field_name, tzname):
         field_name = self._convert_field_to_tz(field_name, tzname)
         sql = self.date_extract_sql(lookup_type, field_name)
diff --git a/django/db/backends/postgresql/operations.py b/django/db/backends/postgresql/operations.py
index 2130571a05..c32ca040e7 100644
--- a/django/db/backends/postgresql/operations.py
+++ b/django/db/backends/postgresql/operations.py
@@ -45,6 +45,11 @@ class DatabaseOperations(BaseDatabaseOperations):
         sql = '(%s)::date' % field_name
         return sql, params
 
+    def datetime_cast_time_sql(self, field_name, tzname):
+        field_name, params = self._convert_field_to_tz(field_name, tzname)
+        sql = '(%s)::time' % field_name
+        return sql, params
+
     def datetime_extract_sql(self, lookup_type, field_name, tzname):
         field_name, params = self._convert_field_to_tz(field_name, tzname)
         sql = self.date_extract_sql(lookup_type, field_name)
diff --git a/django/db/backends/sqlite3/base.py b/django/db/backends/sqlite3/base.py
index 70d511f108..870dc10353 100644
--- a/django/db/backends/sqlite3/base.py
+++ b/django/db/backends/sqlite3/base.py
@@ -210,6 +210,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
         conn.create_function("django_date_extract", 2, _sqlite_date_extract)
         conn.create_function("django_date_trunc", 2, _sqlite_date_trunc)
         conn.create_function("django_datetime_cast_date", 2, _sqlite_datetime_cast_date)
+        conn.create_function("django_datetime_cast_time", 2, _sqlite_datetime_cast_time)
         conn.create_function("django_datetime_extract", 3, _sqlite_datetime_extract)
         conn.create_function("django_datetime_trunc", 3, _sqlite_datetime_trunc)
         conn.create_function("django_time_extract", 2, _sqlite_time_extract)
@@ -403,6 +404,13 @@ def _sqlite_datetime_cast_date(dt, tzname):
     return dt.date().isoformat()
 
 
+def _sqlite_datetime_cast_time(dt, tzname):
+    dt = _sqlite_datetime_parse(dt, tzname)
+    if dt is None:
+        return None
+    return dt.time().isoformat()
+
+
 def _sqlite_datetime_extract(lookup_type, dt, tzname):
     dt = _sqlite_datetime_parse(dt, tzname)
     if dt is None:
diff --git a/django/db/backends/sqlite3/operations.py b/django/db/backends/sqlite3/operations.py
index 4b7fc091db..bf3002b79b 100644
--- a/django/db/backends/sqlite3/operations.py
+++ b/django/db/backends/sqlite3/operations.py
@@ -85,6 +85,10 @@ class DatabaseOperations(BaseDatabaseOperations):
         self._require_pytz()
         return "django_datetime_cast_date(%s, %%s)" % field_name, [tzname]
 
+    def datetime_cast_time_sql(self, field_name, tzname):
+        self._require_pytz()
+        return "django_datetime_cast_time(%s, %%s)" % field_name, [tzname]
+
     def datetime_extract_sql(self, lookup_type, field_name, tzname):
         # Same comment as in date_extract_sql.
         self._require_pytz()
diff --git a/django/db/models/functions/__init__.py b/django/db/models/functions/__init__.py
index 14f1f69d01..dd45d7bb4c 100644
--- a/django/db/models/functions/__init__.py
+++ b/django/db/models/functions/__init__.py
@@ -5,7 +5,7 @@ from .base import (
 from .datetime import (
     Extract, ExtractDay, ExtractHour, ExtractMinute, ExtractMonth,
     ExtractSecond, ExtractWeekDay, ExtractYear, Trunc, TruncDate, TruncDay,
-    TruncHour, TruncMinute, TruncMonth, TruncSecond, TruncYear,
+    TruncHour, TruncMinute, TruncMonth, TruncSecond, TruncTime, TruncYear,
 )
 
 __all__ = [
@@ -16,5 +16,5 @@ __all__ = [
     'Extract', 'ExtractDay', 'ExtractHour', 'ExtractMinute', 'ExtractMonth',
     'ExtractSecond', 'ExtractWeekDay', 'ExtractYear',
     'Trunc', 'TruncDate', 'TruncDay', 'TruncHour', 'TruncMinute', 'TruncMonth',
-    'TruncSecond', 'TruncYear',
+    'TruncSecond', 'TruncTime', 'TruncYear',
 ]
diff --git a/django/db/models/functions/datetime.py b/django/db/models/functions/datetime.py
index 85a398a50b..9cbdcb0231 100644
--- a/django/db/models/functions/datetime.py
+++ b/django/db/models/functions/datetime.py
@@ -239,6 +239,23 @@ class TruncDate(TruncBase):
         return sql, lhs_params
 
 
+class TruncTime(TruncBase):
+    kind = 'time'
+    lookup_name = 'time'
+
+    @cached_property
+    def output_field(self):
+        return TimeField()
+
+    def as_sql(self, compiler, connection):
+        # Cast to date rather than truncate to date.
+        lhs, lhs_params = compiler.compile(self.lhs)
+        tzname = timezone.get_current_timezone_name() if settings.USE_TZ else None
+        sql, tz_params = connection.ops.datetime_cast_time_sql(lhs, tzname)
+        lhs_params.extend(tz_params)
+        return sql, lhs_params
+
+
 class TruncHour(TruncBase):
     kind = 'hour'
 
@@ -252,3 +269,4 @@ class TruncSecond(TruncBase):
 
 
 DateTimeField.register_lookup(TruncDate)
+DateTimeField.register_lookup(TruncTime)