zerokspot+Django: contenttypes and permalinks

As some kind of project for the next couple of months I’ve now started to work on a new implementation of zerokspot.com no longer using a pre-built CMS like WordPress or Drupal but trying to do it completely on my own using Django and several generic apps for it.

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While I’m not sure yet, if this system will really succeed the current Drupal site, it will at least do a couple of things for me:

1. Improve my knowledge about Django and how to work with it
2. Perhaps some style improvements
3. Offer me a general playground for ideas

I also thought for a while to go even deeper and just start from scratch using components like CherryPy, SQLObject and Mako, but I guess this would have been a little bit too hardcore or simply would have taken too much time. I simply prefer to always see a light at the end of the tunnel ;)

So last Wednesday I started writing some code and also some general features I’d like to see in this new implementation like Tagging, RSS/Atom etc. and in this and the following entries I’d like to write a little bit about my progress (whatever this will be worth in the end) and new things I learnt about Django.

Content types

The first things I learned about Django came from taking a look at the Django-tagging’s code: There is a generic way to store model associations for a certain object. Think about following situation: You want to offer a commenting system with your project but don’t want to limit it to , let’s say, the Article model.

This is where the contenttypes app comes in handy. It contains a Model (and therefor a table in your project’s database) that manages all the Models used by your project and let’s you reference them using the content type as foreign keys.

class Comment(models.Model):
	body = models.TextField()
	content_type = models.ForeignKey(ContentType)

ContentType’s manager now offers with the get_for_model now a way to receive the respective foreign keys for a given Model :-)

Something that I haven’t found out yet is, how I could use this, to efficiently have a listing of - for example - the latest 10 content elements created on my site (like reviews, entries etc.). So far I would go about it somehow like this:

1. Extend for example the journal entry model’s safe method with code to automatically create an entry into a global content table. Let’s call this model Node for now.
2. Then I’d fetch the latest n elements from this Node class using the normal Node.objects.order_by('-pub\_date')[:5]
3. Now comes the real problem: How to get to the actual elements without creating tons of queries. I guess the only solution for this for now would be to create temp. lists of IDs for each content type and then do queries on them.

I think I will implement something like this tomorrow just to find out if and how it really works. Might be a nice addition to django.contrib.contenttype’s Manager if it doesn’t exist yet and I just missed it :-)

Permalinks

Another thing I learnt yesterday was, that there also exists a decorator to facilitate the creation of Model specific URLs. One of the first things I learnt about Django was, that there seems to be a convention that model’s should offer a get_absolute_url method in order to explicitly address model instances with an URL.

While a great idea, it becomes a pain to maintain and it would be nice to be able to bind such an object not to an URL per se, but to a method that would be called in order to represent such an object to the user at the other end of the pipe.

This would now be a job for the permalink decorator:

class Entry(models.Model):
	# ...
	
	@models.permalink
	def get_absolute_url(self):
		return ('myproj.myapp.views.view_entry',[],dict(id=self.id),)

This will now do a reverse lookup in the URLs configuration and generate an URL for the given view function.