Fixed #2443 -- Added DurationField.

A field for storing periods of time - modeled in Python by timedelta. It
is stored in the native interval data type on PostgreSQL and as a bigint
of microseconds on other backends.

Also includes significant changes to the internals of time related maths
in expressions, including the removal of DateModifierNode.

Thanks to Tim and Josh in particular for reviews.

1 files changed, 16 insertions, 0 deletions

diff --git a/django/db/backends/__init__.py b/django/db/backends/__init__.py
index bdf841cbd9..104744b220 100644
--- a/django/db/backends/__init__.py
+++ b/django/db/backends/__init__.py
@@ -1,5 +1,6 @@
 from collections import deque
 import datetime
+import decimal
 import time
 import warnings
 
@@ -18,6 +19,7 @@ from django.db.backends.signals import connection_created
 from django.db.backends import utils
 from django.db.transaction import TransactionManagementError
 from django.db.utils import DatabaseError, DatabaseErrorWrapper, ProgrammingError
+from django.utils.dateparse import parse_duration
 from django.utils.deprecation import RemovedInDjango19Warning
 from django.utils.functional import cached_property
 from django.utils import six
@@ -575,6 +577,9 @@ class BaseDatabaseFeatures(object):
 
     supports_binary_field = True
 
+    # Is there a true datatype for timedeltas?
+    has_native_duration_field = False
+
     # Do time/datetime fields have microsecond precision?
     supports_microsecond_precision = True
 
@@ -1251,8 +1256,16 @@ class BaseDatabaseOperations(object):
         Some field types on some backends do not provide data in the correct
         format, this is the hook for coverter functions.
         """
+        if not self.connection.features.has_native_duration_field and internal_type == 'DurationField':
+            return [self.convert_durationfield_value]
         return []
 
+    def convert_durationfield_value(self, value, field):
+        if value is not None:
+            value = str(decimal.Decimal(value) / decimal.Decimal(1000000))
+            value = parse_duration(value)
+        return value
+
     def check_aggregate_support(self, aggregate_func):
         """Check that the backend supports the provided aggregate
 
@@ -1272,6 +1285,9 @@ class BaseDatabaseOperations(object):
         conn = ' %s ' % connector
         return conn.join(sub_expressions)
 
+    def combine_duration_expression(self, connector, sub_expressions):
+        return self.combine_expression(connector, sub_expressions)
+
     def modify_insert_params(self, placeholders, params):
         """Allow modification of insert parameters. Needed for Oracle Spatial
         backend due to #10888.