2

Given the following model I am attempting to use the models ID field (a UUID) in the upload_to path but its defined as None, presumably as it hasn't been generated at that point.

If I use a UUID field that isn't defined as the primary key it works OK.

How do I get the value of the id field at the point picture_path is ran?

# models.py
    
class Foo(models.Model)
    
  def picture_path(instance, filename):  
    return 'pictures/{0}/{1}'.format(instance.id, filename)
    
  id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
  picture = models.ImageField(upload_to=picture_path, null=True, blank=True)

(I know that django will automagically append random chars to avoid duplicate file names, this is a deliberately simplified example, in the real app need to keep each models files in a seperate folder)

Sunderam Dubey
  • 1
  • 11
  • 20
  • 40
Ryan
  • 23,871
  • 24
  • 86
  • 132

1 Answers1

1

Since in your example primary key is generated as uuid4 and does not depend on DB counter - you can safely generate it upfront.

In other words - you don't have to wait for DB insert to get primary key - you can make it yourself and then insert into DB (being pretty sure that it's unique - because it's uuid4)

So, in code the fix will be:

def picture_path(instance, filename):
    instance.id = str(uuid.uuid4())
    return 'pictures/{0}/{1}'.format(instance.id, filename)

Call to picture_path is done before save. And when in save id is populated from outside - it won't be overwritten by Django.

Egor Wexler
  • 1,754
  • 6
  • 22