title: Django models: Only permit one entry in a model?
body: <p>I want to make some of my Django global settings configurable through the admin interface.</p>
  
  <p>To that end, I've decided to set them as database fields, rather than in <code>settings.py</code>.</p>
  
  <p>These are the settings I care about:</p>
  
  <pre><code> class ManagementEmail(models.Model):
      librarian_email = models.EmailField()
      intro_text = models.CharField(max_length=1000)
      signoff_text = models.CharField(max_length=1000)
  </code></pre>
  
  <p>These are one-off global settings, so I only ever want there to be a single <code>librarian_email</code>, <code>intro_text</code> etc floating around the system. </p>
  
  <p>Is there a way I can prevent admin users from adding new records here, <strong>without preventing them from editing the existing record</strong>?</p>
  
  <p>I guess I can do this by writing a custom admin template for this model, but I'd like to know if there's a neater way to configure this.</p>
  
  <p>Could I use something other than <code>class</code>, for example?</p>
  
  <p>Thanks!</p>