title: Why not calling save() on one model, while calling on another
body: <p>I am learning django from <a href="http://www.tangowithdjango.com/book17/" rel="nofollow">tangowithdjango</a>. I am trying to understand the code of <code>populate_rango.py</code>. 
  Code is:</p>
  
  <pre><code>import os
  os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'tango_with_django_project.settings')
  
  import django
  django.setup()
  
  from rango.models import Category, Page
  
  
  def populate():
      python_cat = add_cat('Python')
  
      add_page(cat=python_cat,
          title="Official Python Tutorial",
          url="http://docs.python.org/2/tutorial/")
  
      add_page(cat=python_cat,
          title="How to Think like a Computer Scientist",
          url="http://www.greenteapress.com/thinkpython/")
  
      add_page(cat=python_cat,
          title="Learn Python in 10 Minutes",
          url="http://www.korokithakis.net/tutorials/python/")
  
      django_cat = add_cat("Django")
  
      add_page(cat=django_cat,
          title="Official Django Tutorial",
          url="https://docs.djangoproject.com/en/1.5/intro/tutorial01/")
  
      add_page(cat=django_cat,
          title="Django Rocks",
          url="http://www.djangorocks.com/")
  
      add_page(cat=django_cat,
          title="How to Tango with Django",
          url="http://www.tangowithdjango.com/")
  
      frame_cat = add_cat("Other Frameworks")
  
      add_page(cat=frame_cat,
          title="Bottle",
          url="http://bottlepy.org/docs/dev/")
  
      add_page(cat=frame_cat,
          title="Flask",
          url="http://flask.pocoo.org")
  
      # Print out what we have added to the user.
      for c in Category.objects.all():
          for p in Page.objects.filter(category=c):
              print "- {0} - {1}".format(str(c), str(p))
  
  def add_page(cat, title, url, views=0):
      p = Page.objects.get_or_create(category=cat, title=title)[0]
      p.url=url
      p.views=views
      p.save()
      return p
  
  def add_cat(name):
      c = Category.objects.get_or_create(name=name)[0]
      return c
  
  # Start execution here!
  if __name__ == '__main__':
      print "Starting Rango population script..."
      populate()
  </code></pre>
  
  <p>What am I unable to understand is, the add_cat function doesn't call save:</p>
  
  <pre><code>def add_cat(name):
  c = Category.objects.get_or_create(name=name)[0]
  return c
  </code></pre>
  
  <p>while, add_page calls p.save():</p>
  
  <pre><code>def add_page(cat, title, url, views=0):
      p = Page.objects.get_or_create(category=cat, title=title)[0]
      p.url = url
      p.views = views
      p.save()
      return p
  </code></pre>
  
  <p>Please explain this to me.</p>