title: Django model - object attribute update after creation
body: <p>I am working on some Django project (first time) and after lot of searching i have no clue how to proper update object attribute after creation. I have sucha models.py</p>
  
  <pre><code>    from django.db import models
  import os
  
  
  # Create your models here.
  
  class Place(models.Model):
      # Build paths inside the project like this: os.path.join(BASE_DIR, ...)
      BASE_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
      # Add templates folder for dynamic usage, os independent
      TEMPLATE_DIR = os.path.join(BASE_DIR, "templates/places")
  
      name = models.CharField(max_length=100, unique=True)
      display_name = models.CharField(max_length=100)
      floor = models.DecimalField(max_digits=3, decimal_places=0)
      template = models.FilePathField(path=TEMPLATE_DIR, match=".*html")
      url = models.URLField(unique=True)
  
  # Display name of object in object list view
      def __str__(self):
          return self.name
  </code></pre>
  
  <p>Question is how to update <strong>url</strong> attribute after object creation of url to this particular object, it should be something like (base url + object_id i know object_id is created after object creation) but after searching documentation i dont have ideas how to do this properly.</p>
  
  <p>I tried <strong>get_absolute_path</strong> but with no success.</p>
  
  <p>Maybe some kind <strong>post_save</strong> method override ?</p>