title: Filter ForeignKey choices in an Admin Form based on selections in same models ManytoMany Field?
body: <p>I am making a &quot;matches&quot; model that currently has these fields in them:</p>
  <pre><code>event = models.ForeignKey(Event, on_delete=models.RESTRICT)
  match_participants = models.ManyToManyField(Wrestler, on_delete=models.RESTRICT, null=True, blank=True,)
  match_type = models.CharField(max_length=25, choices=match_choices, default=BLOCK)
  match_result = models.CharField(max_length=25, choices=result_choices, default=NOT_OC)
  winner = models.ForeignKey(Wrestler, on_delete=models.RESTRICT, null=True, blank=True, related_name=&quot;winner&quot;)
  </code></pre>
  <p>In my scenario the &quot;winner&quot; can only be one of the foreignkeys chosen in &quot;match_participants&quot;, I would really like to filter the winner field to only those chosen foreignkeys. Is this possible? I know you can filter foreign key selections based on entries into other models, but not too sure about same table entry.</p>
  <p>Here's a UML example of what my database structure currently is:</p>
  <p><a href="https://i.stack.imgur.com/AIg3o.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AIg3o.jpg" alt="enter image description here" /></a></p>