Django ImageField and FileField dynamic upload path in Newforms Admin

I’ve been using Scott’s CustomImageField for quite some time, but recently it stopped working when I moved to Newforms Admin. I wasn’t really sure why this was, but decided to build a quick workaround for now so I can continue to use the newforms-admin.

Scott’s Field used the post_init and pre_save signals, which is probably the right way… Since this wasn’t working anymore, I decided to use the post_save signal. This way the image or file would be saved to a temporary directory initially and then moved to the appropriate directory afterwards.

Here is how the field would be defined in the model:

    class Image(models.Model):
	file = CustomImageField(use_key=True, upload_to='tmp')

use_key and upload_to are optional. use_key defaults to False. If it is True then the id of the instance will be used as a prefix for the new file as there is the potential for overwriting now that we are moving the file. upload_to will simply define the temporary directory to upload the files to initially.

Below is the code that defines the CustomImageField. I have this in a file called “custom_fields.py.”

from django.db.models import ImageField, FileField, signals
from django.dispatch import dispatcher
from django.conf import settings
import shutil, os, glob, re
from distutils.dir_util import mkpath

class CustomImageField(ImageField):
    """Allows model instance to specify upload_to dynamically.

    Model class should have a method like:

        def get_upload_to(self, attname):
            return 'path/to/%d' % self.id

    Based closely on: http://scottbarnham.com/blog/2007/07/31/uploading-images-to-a-dynamic-path-with-django/
    """
    def __init__(self, *args, **kwargs):
        if not 'upload_to' in kwargs:
            kwargs['upload_to'] = 'tmp'
        self.use_key = kwargs.get('use_key', False)
        if 'use_key' in kwargs:
            del(kwargs['use_key'])
        super(CustomImageField, self).__init__(*args, **kwargs)

    def contribute_to_class(self, cls, name):
        """Hook up events so we can access the instance."""
        super(CustomImageField, self).contribute_to_class(cls, name)
        dispatcher.connect(self._move_image, signal=signals.post_save, sender=cls)

    def _move_image(self, instance=None):
        """
            Function to move the temporarily uploaded image to a more suitable directory 
            using the model's get_upload_to() method.
        """
        if hasattr(instance, 'get_upload_to'):
            src = getattr(instance, self.attname)
            if src:
                m = re.match(r"%s/(.*)" % self.upload_to, src)
                if m:
                    if self.use_key:
                        dst = "%s/%d_%s" % (instance.get_upload_to(self.attname), instance.id, m.groups()[0])
                    else:
                        dst = "%s/%s" % (instance.get_upload_to(self.attname), m.groups()[0])
                    basedir = "%s%s/" % (settings.MEDIA_ROOT, os.path.dirname(dst))
                    mkpath(basedir)
                    shutil.move("%s%s" % (settings.MEDIA_ROOT, src),"%s%s" % (settings.MEDIA_ROOT, dst))
                    setattr(instance, self.attname, dst)
                    instance.save()

    def db_type(self):
        """Required by Django for ORM."""
        return 'varchar(100)'

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