title: How to enforce different values in multiple ForeignKey fields for Django
body: <p>I have the following models in Django:</p>
  
  <pre><code>from django.db import models
  
  class Team(models.Model):
      name = models.CharField(max_length=200)
  
  
  class Match(models.Model):                                                      
      team_home = models.ForeignKey(Team)                                                      
      team_visitors = models.ForeignKey(Team)                                                       
      league = models.CharField(max_length=200)                                                      
      date_played = models.DateField()  
  </code></pre>
  
  <p>The idea is to be able to have a 'Match' object which has two teams who played a match of some game. It would be very odd that a team be playing itself. How can I guarantee that <code>team_home</code> is not equal to <code>team_visitors</code>?</p>