gistfile1.pyw

import os

from django.core.files.storage import FileSystemStorage
from django.db.models import signals

class MyFileSystemStorage(FileSystemStorage):
    def rename(self, src, dest):
        return os.rename(self.path(src), self.path(dest))

class MyFileField(models.FileField):
    def __init__(self, *args, **kwargs):
        super(MyFileField, self).__init__(*args, **kwargs)
        self.storage = MyFileSystemStorage()
    
    def pre_save(self, model_instance, add):
        file = getattr(model_instance, self.attname)

        filename = self.upload_to(model_instance, file.name)
        
        if file and file._committed:    
            if file.name != filename:
                file.storage.rename(file.name, filename)
        
        file.name = filename
        
        return file
    
    def save_file(self, instance, sender, **kwargs):
        file = getattr(instance, self.attname)

        if file and not file._committed:
            filename = self.upload_to(instance, file.name)
            file.save(filename, file, save=file.name!=filename)
        return file
        
    def contribute_to_class(self, cls, name):
        super(MyFileField, self).contribute_to_class(cls, name)
        signals.post_save.connect(self.save_file, sender=cls)
                        
class MyModel(models.Model):
    title = models.CharField(max_length=200)
    file = MyFileField(upload_to=lambda instance, filename: 'files/%s_%s' % (instance.pk, instance.title))