Thoughts on web programming and the world of technology

January 17, 2012, reading time: 2 minutes

Upgrading your Django media files to use a CDN

I was using django-filebrowser on a project and my Rackspace VM quickly ran out of disk space. Since the site isn’t getting much traffic at all, I didn’t want to pay extra for a bigger VM. Instead, I decided to move all of the user uploaded media to Rackspace Cloudfiles. It’s super cheap and they have a nice API.

Now, the challenge was to make the transition from a filebrowser-based system. First of all, I knew I was going to use django-storages as the new storage class for my class. I played around with it on the side and it worked like a charm.

Next, I wrote a quick little Python script to upload all of the files to Cloudfiles. Since the filenames didn’t change at all, I could just write a South migration that would strip the /uploads part and be done with it.

I had a look at the Django documentation to see what exactly a FileField was. It turns out it takes a Django File object which in turn is a thin wrapper around the Python built-in file object. This didn’t sound exactly easy to do. I would have to open a remote file with Python’s open(‘file.mp3’) and have Django inspect it for size and file type. This is clunky at best if you remember that this will have to live in a South migration.

Also worth noting is the fact that filebrowser’s model field is a subclass of CharField and has no special file-related properties or methods.

You can’t use the DEFAULT_STORAGE_CLASS setting because filebrowser will start yelling at you. Instead, you specify the storage class right in the new model field.

from storages.backends.mosso import cloudfiles_upload_to, CloudFilesStorage
cloudfiles_storage = CloudFilesStorage()

class Item(models.Model):
    old_field = FileBrowseField(max_length=500, blank=True)
    new_field = models.FileField(upload_to=cloudfiles_upload_to,
            storage=cloudfiles_storage, default='')

Now you can go and write your migration and Django won’t yell at you. Now we go back to the problem outlined above. How do you create an instance of File to pass to item.new_field.

After hours of reading the source and debugging, I realized that you can simply pass in the filename as a string and the storage class will do the right thing. It’s actually really simple and painless. Your data migration might look something like:

for item in orm.Item.objects.all():
    item.new_field = os.path.basename(item.old_field.url)
    item.save()

So, I was already somewhat overjoyed that this would in fact be easy and then I discovered that the change from filebrowser to django-storages doesn’t require a schema migration. This means that if your file names are the same there is no database change needed at all. How cool is that?