Custom model field change base of id

Question

I am trying to get a base 36 string to use in my URLs. I have written a function that converts a number to base 36, using letters to represent digits higher than 9. I am trying to find a good way to set the default value of a character field equal to this function, but I am not sure how to get the Django default primary key value into it. Any ideas?

I would think I could just put something like this into my model, but it does not work:

base_36 = models.TextField(default=convert_base(id, 36))

Answer 1

You could either:

1. Override your model's save() method:

   class YourModel(models.Model):
   
       base_36 = models.TextField()
   
       def save(self, *args, **kwargs):
           # will assign a value to pk
           super(YourModel, self).save(*args, **kwargs)
           # convert the pk to base 36 and save it in our field
           self.base_36 = convert_base(self.pk, 36)
           self.save()
   

2. Turn your base_36 field into a property:

   class YourModel(models.Model):
   
       @property
       def base_36(self):
           return convert_base(self.pk,36)
   
   # can call a property just like a field:
   # print YourModel.objects.get(pk=1).base_36
   

Answer 2

If I understand correctly you want to use a CharField as a primary key and need to redefine the way django generates its value for new objects.

I think that you would complicate your life if you proceed in that way. Instead you can use base36 identifiers only in URLs and let your view translate them into the integer corresponding to the usual primary key, as in:

def my_view(request,base32_id):
   pk = base32_to_int(base32_id)
   obj = Model.objects.get(pk=pk)
   ...