This document discusses Django middleware and provides an example of a custom middleware class called DBLogMiddleware. It summarizes that Django middleware can be used to handle common tasks like sessions, caching, authentication, and more. It then demonstrates how to create a custom middleware class to log exceptions to a database. The DBLogMiddleware class processes exceptions by recording error details, traceback, and server information to database models.

1. Know your namespace
A peek inside a django namespace.
(and an open source project implementation: django-db-log)

2. django.middleware

3. Pluggable

4. why do i care?
simple dummy...

5. available middleware provides:
• session handling • internationalization
• caching • db transactions
• authentication • gzip compression
• flat pages • etc.

6. ...umm, yea i could use those.

7. activating middleware
MIDDLEWARE_CLASSES = (
'django.middleware.common.CommonMiddleware',
'django.contrib.sessions.middleware.SessionMiddleware',
'django.contrib.auth.middleware.AuthenticationMiddleware',
'django.middleware.doc.XViewMiddleware',
)

8. need a custom solution?

9. easy as pie

10. Simple Guidelines
• don’t have to subclass anything
• live anywhere on the python path
(reusable!)
• must define one or more of these 4
methods...

11. feeling the flow, being the ball
process process process
call view
request view response
exception?
process
exception

12. Real World Example

13. from models import Error, ErrorBatch
import traceback
import socket
import warnings
Look mom, no hands!
import md5
class DBLogMiddleware(object):
def process_exception(self, request, exception):
server_name = socket.gethostname()
tb_text = traceback.format_exc()
class_name = exception.__class__.__name__
checksum = md5.new(tb_text).hexdigest()
defaults = dict(
class_name = class_name,
message = exception.message,
url = request.build_absolute_uri(),
server_name = server_name,
traceback = tb_text,
)
try:
Error.objects.create(**defaults)
batch, created = ErrorBatch.objects.get_or_create(
class_name = class_name,
server_name = server_name,
checksum = checksum,
defaults = defaults
)
if not created:
batch.times_seen += 1
batch.save()
except Exception, exc:
warnings.warn(unicode(exc))

14. Discussion
• http://code.google.com/p/django-db-log/
• http://www.davidcramer.net/
• http://www.djangoproject.com/documentation/middleware/