Question

I have a Model containing a FileField.
I’d like this FileField to have a unique path.

At first, at though about using the ID of the entry, but Django move the file to it’s upload_to path before saving the entry, so ID is empty.

Moreover, I can’t use something like the title or any other elements of the model (except the creation date) since they can be changed by the user. And I prefer not to copy/delete a file every time a user change the title of it’s entry (if I use the title as a part of my path).

Here start my research, I found these :

• Generate a unique key and compare it to the database. While the key exist, we generate a new one (Django, unique field generation) : The problem is the potentials hits the while could do to the database before having a unique key

• Getting the timestamp from the creation date. The problem here, is if two people add a file at the exact same time, it will generate conflicts

I’d like to have this unique ID a small as possible, max length of 7 would be great. The perfect solution would have been to have the ID of the entry. Do you know a workaround to do so (calling save() before moving files to their upload_to folder?) or if not, which implementation would be the best, based on one of my solutions or a one you think is better?

Answer 1

Since FileField is, by default, with null=True, blank=True, a possibility is to save the model twice, first by removing the file value (=None), saving, and then, adding the the file value (that was previously stored in a temporary var), and save again.

Here is the code

# this method goes in your model
def save(self, *args, **kwargs):
    # ignoring the double save if this is an update or if there is no files
    if self.pk or not self.file:
        return super(MyModel, self).save(*args, **kwargs)

    old_file = self.file._file
    self.file = None

    super(MyModel, self).save(*args, **kwargs)

    self.file = old_file

    return super(MyModel, self).save(*args, **kwargs)

Well, of course, this will result in a double request to the database when you create a new entry, but any other solution I could come up with required to do at least one hit to the database (key based with unique constraint, key based on the creation date, etc).

Hope this helps!