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.


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 :-)

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.

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