Refs #25774, #26348 -- Allowed Trunc functions to operate with time fields.

Thanks Josh for the amazing testing setup and Tim for the review.

2 files changed, 74 insertions, 8 deletions

diff --git a/docs/ref/models/database-functions.txt b/docs/ref/models/database-functions.txt
index d6c48f966c..20ceadde91 100644
--- a/docs/ref/models/database-functions.txt
+++ b/docs/ref/models/database-functions.txt
@@ -288,8 +288,10 @@ We'll be using the following model in examples of each function::
     class Experiment(models.Model):
         start_datetime = models.DateTimeField()
         start_date = models.DateField(null=True, blank=True)
+        start_time = models.TimeField(null=True, blank=True)
         end_datetime = models.DateTimeField(null=True, blank=True)
         end_date = models.DateField(null=True, blank=True)
+        end_time = models.TimeField(null=True, blank=True)
 
 ``Extract``
 -----------
@@ -500,13 +502,14 @@ but not the exact second, then ``Trunc`` (and its subclasses) can be useful to
 filter or aggregate your data. For example, you can use ``Trunc`` to calculate
 the number of sales per day.
 
-``Trunc`` takes a single ``expression``, representing a ``DateField`` or
-``DateTimeField``, a ``kind`` representing a date part, and an ``output_field``
-that's either ``DateTimeField()`` or ``DateField()``. It returns a datetime or
-date, depending on ``output_field``, with fields up to ``kind`` set to their
-minimum value. If ``output_field`` is omitted, it will default to the
-``output_field`` of ``expression``. A ``tzinfo`` subclass, usually provided by
-``pytz``, can be passed to truncate a value in a specific timezone.
+``Trunc`` takes a single ``expression``, representing a ``DateField``,
+``TimeField``, or ``DateTimeField``, a ``kind`` representing a date or time
+part, and an ``output_field`` that's either ``DateTimeField()``,
+``TimeField()``, or ``DateField()``. It returns a datetime, date, or time
+depending on ``output_field``, with fields up to ``kind`` set to their minimum
+value. If ``output_field`` is omitted, it will default to the ``output_field``
+of ``expression``. A ``tzinfo`` subclass, usually provided by ``pytz``, can be
+passed to truncate a value in a specific timezone.
 
 Given the datetime ``2015-06-15 14:30:50.000321+00:00``, the built-in ``kind``\s
 return:
@@ -616,6 +619,61 @@ that deal with date-parts can be used with ``DateField``::
     2016-01-01 00:00:00+11:00 1
     2014-06-01 00:00:00+10:00 1
 
+``TimeField`` truncation
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. versionadded:: 1.11
+
+.. class:: TruncHour(expression, output_field=None, tzinfo=None, **extra)
+
+    .. attribute:: kind = 'hour'
+
+.. class:: TruncMinute(expression, output_field=None, tzinfo=None, **extra)
+
+    .. attribute:: kind = 'minute'
+
+.. class:: TruncSecond(expression, output_field=None, tzinfo=None, **extra)
+
+    .. attribute:: kind = 'second'
+
+These are logically equivalent to ``Trunc('time_field', kind)``. They truncate
+all parts of the time up to ``kind`` which allows grouping or filtering times
+with less precision. ``expression`` can have an ``output_field`` of either
+``TimeField`` or ``DateTimeField``.
+
+Since ``TimeField``\s don't have a date component, only ``Trunc`` subclasses
+that deal with time-parts can be used with ``TimeField``::
+
+    >>> from datetime import datetime
+    >>> from django.db.models import Count, TimeField
+    >>> from django.db.models.functions import TruncHour
+    >>> from django.utils import timezone
+    >>> start1 = datetime(2014, 6, 15, 14, 30, 50, 321, tzinfo=timezone.utc)
+    >>> start2 = datetime(2014, 6, 15, 14, 40, 2, 123, tzinfo=timezone.utc)
+    >>> start3 = datetime(2015, 12, 31, 17, 5, 27, 999, tzinfo=timezone.utc)
+    >>> Experiment.objects.create(start_datetime=start1, start_time=start1.time())
+    >>> Experiment.objects.create(start_datetime=start2, start_time=start2.time())
+    >>> Experiment.objects.create(start_datetime=start3, start_time=start3.time())
+    >>> experiments_per_hour = Experiment.objects.annotate(
+    ...    hour=TruncHour('start_datetime', output_field=TimeField()),
+    ... ).values('hour').annotate(experiments=Count('id'))
+    >>> for exp in experiments_per_hour:
+    ...     print(exp['hour'], exp['experiments'])
+    ...
+    14:00:00 2
+    17:00:00 1
+
+    >>> import pytz
+    >>> melb = pytz.timezone('Australia/Melbourne')
+    >>> experiments_per_hour = Experiment.objects.annotate(
+    ...    hour=TruncHour('start_datetime', tzinfo=melb),
+    ... ).values('hour').annotate(experiments=Count('id'))
+    >>> for exp in experiments_per_hour:
+    ...     print(exp['hour'], exp['experiments'])
+    ...
+    2014-06-16 00:00:00+10:00 2
+    2016-01-01 04:00:00+11:00 1
+
 ``DateTimeField`` truncation
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/docs/releases/1.11.txt b/docs/releases/1.11.txt
index 2359eec910..392ded70b8 100644
--- a/docs/releases/1.11.txt
+++ b/docs/releases/1.11.txt
@@ -198,6 +198,9 @@ Models
 * :class:`~django.db.models.ImageField` now has a default
   :data:`~django.core.validators.validate_image_file_extension` validator.
 
+* Added support for time truncation to
+  :class:`~django.db.models.functions.datetime.Trunc` functions.
+
 Requests and Responses
 ~~~~~~~~~~~~~~~~~~~~~~
 
@@ -263,7 +266,12 @@ Backwards incompatible changes in 1.11
 Database backend API
 --------------------
 
-* ...
+* The ``DatabaseOperations.time_trunc_sql()`` method is added to support
+  ``TimeField`` truncation. It accepts a ``lookup_type`` and ``field_name``
+  arguments and returns the appropriate SQL to truncate the given time field
+  ``field_name`` to a time object with only the given specificity. The
+  ``lookup_type`` argument can be either ``'hour'``, ``'minute'``, or
+  ``'second'``.
 
 Dropped support for PostgreSQL 9.2 and PostGIS 2.0
 --------------------------------------------------