Next target’s “iphone stopwatch” (:

Please check out the App at http://www.ganjianwei.com/iphone/weiwatch/ or go straight to WeiWatch in the App Store.

Thanks for all the support everyone, hope you like the app!

There’s more to the App including a cute stopwatch minigame I created as well as prompts comparing your newest timing to the average. I’ll be writing more about that soon. Also, I plan to use Apple’s ad-hoc distribution to let some kind folks test it. Let me know if you have an iPhone/iPod touch and are interested in helping me try it out.

Meanwhile, here’s a screenshot of the first screen you see when you open the app:

Also see rankophilia, same thing…

Here’s links to Alex’s and Caleb’s sites:

• http://rankophilia.dorm.duke.edu/
• http://rankophilia.wordpress.com/

Here’s a link to our beloved site: http://rankophilia.dorm.duke.edu/index.php, and this too: http://rankophilia.dorm.duke.edu/rankophiliacs

Touché.

Dealing with foreign keys to abstract model classes

I had an UploadedItem abstract model class and I wanted to let people comment on UploadedItems. In an ideal world, I would be able to write the Comment model class like this:

class Comment(models.Model):
    comment = models.TextField()
    uploader = models.ForeignKey(User)
    upload_date = models.DateTimeField("Date uploaded", editable=True)
    uploaded_item = models.ForeignKey(UploadedItem)

But then you’d get an error saying that you can’t specify an abstract class as a foreign key, which makes sense since Django doesn’t actually implement the abstract model class in the database.

Solution:

The contenttypes framework! More specifically, generic relations. In the end comment looks like this:

class Comment(models.Model):
    comment = models.TextField()
    uploader = models.ForeignKey(User)
    upload_date = models.DateTimeField("Date uploaded", editable=True)

    # Following fields are required for using GenericForeignKey
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    uploaded_item = generic.GenericForeignKey()

Also, to get the reverse relation from my UploadedItem instances such as Announcement, I had to include a comments GenericRelation field in each of the UploadedItem instances where I wanted to allow comments for.

class Announcement(UploadedItem):
    """Announcement"""
    announcement = models.TextField()
    comments = generic.GenericRelation(Comment)

So now, to get all the comments for an announcement, all I would have to do is:

>>> announcement.comments.all()

It might not be the simplest solution, but it really is simple enough, and after I followed instructions from the documentation, it really just worked. Pity I couldn’t have it the “ideal” way, but then again using the contenttypes framework made the final implementation simple enough.

(Next post on making models and forms dynamic)

I also just came across this article on The New York Times about a start-up that rents college textbooks. It’s incredible how such an obvious inefficiency that’s plain for all to see can be the spark for such a successful start-up. We’re often blind to such glaring problems. Don’t get me wrong, we surely notice the inefficiency, just that we try to ignore it, try to get around it and get on with our lives because it would be painful to dwell on every single problem like that since there are an uncountable number out there.

In a way, it’s harder to see problems than their solutions. Most people prefer to remain in denial about problems. It’s obvious why: problems are irritating. They’re problems! Imagine if people in 1700 saw their lives the way we’d see them. It would have been unbearable. This denial is such a powerful force that, even when presented with possible solutions, people often prefer to believe they wouldn’t work.

- Paul Graham

I’ll be looking for these problems now, and when I find them, asking the right questions about why they are problems, and asking the right questions on how to solve them. Hopefully this will get me started on something worthwhile.

Please support this petition to repeal the exemption of marital rape from being charged as rape. Also, if you feel as strongly about this injustice as I do, please invite your friends to sign the petition as well.