Pickling and caching the current request.user, good or bad idea?

[Kevin]

In my attempts to lower database hits, I found that on most of my
pages, auth_user is hit every time. I had an idea about caching this
object in the current session. Is this a good idea, or will it cause
more problems than it helps? If so, what type of problems will I be
looking at?

My app rarely modifies the auth_user table, if at all. Here is a
quick middleware I wrote to go aloneside the current
AuthenticationMiddleware, and it works perfectly! Only 2 database
hits when viewing an account page. One hit to the session table, and
other hit to the table which holds various account settings.

class UserPickleMiddleware(object):
def process_request(self, request):
if 'cached_user' not in request.session:
from django.contrib.auth import get_user
request.session['cached_user'] = get_user(request)
request._cached_user = request.session['cached_user']
return None

I place this just before the standard AuthenticationMiddleware. I
will continue to run tests and see how it functions, if say the user
is added or removed from a group.

My sessions are stored in a database, which makes this interesting.
As it's only hitting the database once to grab both the session and
current user information.

[Kevin]

Okay, so the last one there had a hickup, users could not longer
login, once they have logged out. It kept the AnonymousUser cached...

Here is an update which works with logging back in:

class UserPickleMiddleware(object):
def process_request(self, request):
if 'cached_user' not in request.session:
from django.contrib.auth import get_user

user = get_user(request)
if isinstance(user, User):
request.session['cached_user'] = user
if 'cached_user' in request.session:

request._cached_user = request.session['cached_user']
return None

This one makes sure that the user instance is indeed a regular User
and not some Anonymous person before setting the cached data. The
code could be more optimized. I didn't use an Else, because it's
needs to set the request variables. I'd rather write an extra "if"
instead of copying the same line to set the request variable twice.