DatabaseCache doesn't work if database backend returns datetime values as strings

[Michael Manfre]

DatabaseCache intentionally uses cursors and converts all datetimes to naive values. This is a problem for database backends that return datetimes from the database as strings that must be converted to a datetime before being used. All reads of the expires column should be passed through DatabaseOperations.convert_values, and timezone.make_naive to maintain the current naive-only datetimes behavior.

[Michael Manfre]

​https://github.com/django/django/pull/1676

Patch uses typecast_timestamp and checks existing DatabaseFeature.needs_datetime_string_cast to match behavior of SQLCompiler without using too much of the ORM.

[Anssi Kääriäinen <akaariai@…>]

In d5606b57637f00c4349732d79541faa41acfe29c:

Fixed #21146 - DatabaseCache converts expires to python value

DatabaseCache uses raw cursors to bypass the ORM. This prevents it from
being used by database backends that require special handling of datetime
values.

There is no easy way to test this, so no tests added.

[Anssi Kääriäinen <akaariai@…>]

In a979a2fea5415849773fdfb37765ffedef6f50f2:

[1.6.x] Fixed #21146 - DatabaseCache converts expires to python value

DatabaseCache uses raw cursors to bypass the ORM. This prevents it from
being used by database backends that require special handling of datetime
values.

There is no easy way to test this, so no tests added.

Backport of d5606b5763 from master