# Django 2.1.8.dev20190330215650 documentation

# Django 1.8.2 release notes

May 20, 2015

Django 1.8.2 fixes a security issue and several bugs in 1.8.1.

## Fixed session flushing in the `cached_db` backend

A change to `session.flush()` in the `cached_db` session backend in Django 1.8 mistakenly sets the session key to an empty string rather than `None`. An empty string is treated as a valid session key and the session cookie is set accordingly. Any users with an empty string in their session cookie will use the same session store. `session.flush()` is called by `django.contrib.auth.logout()` and, more seriously, by `django.contrib.auth.login()` when a user switches accounts. If a user is logged in and logs in again to a different account (without logging out) the session is flushed to avoid reuse. After the session is flushed (and its session key becomes `''`) the account details are set on the session and the session is saved. Any users with an empty string in their session cookie will now be logged into that account.

## Bugfixes

- Fixed check for template engine alias uniqueness (#24685).
- Fixed crash when reusing the same `Case` instance in a query (#24752).
- Corrected join promotion for `Case` expressions. For example, annotating a query with a `Case` expression could unexpectedly filter out results (#24766).
- Fixed negated `Q` objects in expressions. Cases like `Case(When(~Q(friends__age__lte=30)))` tried to generate a subquery which resulted in a crash (#24705).
- Fixed incorrect GROUP BY clause generation on MySQL when the query's model has a self-referential foreign key (#24748).
- Implemented `ForeignKey.get_db_prep_value()` so that `ForeignKey`s pointing to `UUIDField` and inheritance on models with `UUIDField` primary keys work correctly (#24698, #24712).
- Fixed `isnull` lookup for `HStoreField` (#24751).
- Fixed a MySQL crash when a migration removes a combined index (unique_together or index_together) containing a foreign key (#24757).
- Fixed session cookie deletion when using `SESSION_COOKIE_DOMAIN` (#24799).
- On PostgreSQL, when no access is granted for the `postgres` database, Django now falls back to the default database when it normally requires a "no database" connection (#24791).
- Fixed display of `contrib.admin`’s `ForeignKey` widget when it's used in a row with other fields (#24784).