This Week in Django 21

This Week in Django is a weekly podcast about all things Django.

This week we have a couple of special guests. First, Eric Florenzano joins us for most of the show, and provides special insight into a few conversation items. Secondly we privileged to have Francis Cleary on the program to discuss a couple Tip of the Week items. We also cover all the regular stuff plus stream the program live on ustream.

Please see the Show Notes below for all the pertinent information and links

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Show Notes

• Streaming the Show Live on UStream
  If you want to watch us do the show including show prep stuff follow Brian Rosner on Twitter for notifications.

Tracking Trunk (2:50)

• Allow Query objects to be values in filters (7494) – This has use with update statements. Problem remained in MySQL with a test in 7495 and a fix for nested updates in 7496.

• Allow QuerySets and Query objects to be pickled and unpickled (7499) – Pickle Query when you only want to recreate the necessary information to recreate the QuerySet, otherwise pickle the QuerySet.

• Fixed problem with double-negation queries on Oracle (7509)

Branching & Merging (8:53)

• Allow a formset to be passed through _inlineformset_factory. (7508)

• Implemented change history for the admin (7507) – This includes the ability to track changes on a newform. Model formsets now only return the changed/new objects saved. A big thanks to Karen Tracey and Alex Gaynor.

Community Catchup (19:38)

• Django l10n – Marc Garcia, who was on last week’s show provides a followup post that does a great job of pulling together the information we discussed as well as stuff we did not get time to cover.

• jQuery style chaining with the Django ORM – Informative post by Simon Willison that discusses the chaining capabilities of the ORM as well as an interesting approach to expanding the QuerySet methods.
  • Snippet 734 on QuerySetManager

• Inheritance vs. Composition – Excellent post by Eric Florenzano on the differences between inheritance and composition approaches to structuring your models in Django.

• An interview with Russell Keith-Magee – Django core contributor – Another great interview by Shabda Raaj at the 42 Topics Blog.

Tip of the Week (36:16)

Francis Cleary is on the show with us this week to present his tip that he entered in the Win Cool Stuff Contest and was our grand prize winner.

Multiple view prefixes

Rather then have complex and long urls like so

urlpatterns += patterns('',
   (r'^$', 'mySite.Project.views.mainpage' ),
   (r'^custom/view/$', 'mySite.Project.views.'view_function'),
   (r'^lookup/tag/(?P\w+)/$', 'mySite.Project.views.tag_list'),
   (r'^users/$' , 'django.views.generic.list_detail.object_list', user_dict),
   (r'^recent/$','django.views.generic.list_detail.object_list', all_dict),
   (r^text/$', 'django.views.generic.date_based.object_detail', object_dict),
)

Take advantage of the first argument to the patterns() function to specify a prefix to apply to each view function. just make sure you have the += not just =.

urlpatterns += patterns('mySite.Project.views',
   (r'^$', 'mainpage'),
   (r'^custom/view/$', 'view_function'),
   (r'^lookup/tag/(?P\w+)/$', 'tag_list'),
)

urlpatterns += patterns(‘django.views.generic’,

   (r’^users/$’ , ‘list_detail.object_list’, user_dict),

   (r’^recent/$’, ‘list_detail.object_list’, all_dict),

   (r’^(?P\d{4})/$’, ‘date_based.archive_year’, object_dict),

)

• Django Documentation on Multiple View Prefixes

Advanced Generic Views

If you don’t want your urls.py filling up with dictionary or would like to do more complicated filtering or extra work to a list. Define view functions that return your generic view and dictionary.

In this example from the Django Book. We will use a generic view to
display an author but we want to update the last_accessed data.

urls.py

from mysite.books.views import author_detail

urlpatterns = patterns(’’,

   #...

   (r’^authors/(?Pd+)/$’, author_detail),

)

views.py

import datetime

from mysite.books.models import Author

from django.views.generic import list_detail

from django.shortcuts import get_object_or_404

def author_detail(request, author_id):

   # Look up the Author (and raise a 404 if she’s not found)

   author = get_object_or_404(Author, pk=author_id)


Record the last accessed date

   author.last_accessed = datetime.datetime.now()

   author.save()



Show the detail page

   return list_detail.object_detail(

       request,

       queryset = Author.objects.all(),

       object_id = author_id,

   )

Rather then calling the generic view from the urls.py you can once
again see how uncoupled things are in django and just return the
generic view from your own wrapped view.

• Django tips: get the most out of generic views – Great post on wrapping generic views by James Bennett.

• Are you generic? – Great earlier post by Wilson Miner on using Generic Views for non-programmers.

IRC Ad Nauseam (45:33)

Django IRC FAQ

Backwards Incompatible Changes Information

• We have discussed the changes to the Paginator that occured during the PyCon 2008 sprints, but we are still seeing people tripping up over it. Paginator originally worked only on QuerySets, but has now been abstracted out. Paginiator is now generalized enough to work on lists. This is the reason for QuerySetPaginator. It special cases certain things to prevent performing the wrong operation on the QuerySet.

>>> from cameras.models import CameraImage
>>> CameraImage.objects.all().count()
248788L
>>> from django.core.paginator import Paginator 
>>> paginator = Paginator( CameraImage.objects.all(), 48, True)
>>> import time;start=time.time(); page = paginator.page(50); print time.time()-start
17.4773068428

Some questions about general IRC

We get lots of questions about IRC in general, so maybe a few little tidbits here and there:

Why don’t you use manners? When I say Thank You, you don’t respond.

Okay here’s the deal, there’s no reason to increase the noise level on IRC. That means although we appreciate the thanks, often we will not acknowledge it. So don’t take it personally.

I asked a question and no one responded. Why is that?

People will answer if they know. You can re-ask but please wait a bit. Don’t use the #django-dev channel, that’s the wrong thing to do.

It might be good to think about how you can rephrase the question.

Use the Django-Users Mailing list. It’s another avenue available.

Can anyone help with a NewForms-Admin Question?

Don’t ask to ask. Just ask straight away. It depends often on the area of the question. So it’s best to just ask your question.

Will “blank” work?

Try it. Often the best thing to do is try it. That’s what anyone will end up doing.

Couple other tips, read the FAQ, Backwards Incompatible Changes, and the Freenode FAQ.

Thank You! (58:20)