title: List_display for ManytoMany fields in Admin panel
body: <p>I have 2 apps: <code>Visitors</code> and <code>Meetings</code>, linked via a <code>ManytoMany</code> field:</p>
  
  <p>visitors/models.py:</p>
  
  <pre><code>from django.db import models
  from meetings.models import Meeting
  
  class Visitor(models.Model):
  
      visitor_name = models.CharField(default='name', max_length=128, blank=False, null=False)
      visitor_meetings = models.ManyToManyField(Meeting)
  
      def __str__(self):
          return self.visitor_name
  </code></pre>
  
  <p>meetings/models.py:</p>
  
  <pre><code>from django.db import models
  from team.models import Team
  
  class Meeting(models.Model):
      team_member = models.ForeignKey(Team)
      meeting_name = models.CharField(default='name', max_length=128, blank=True, null=True)
  
      def __str__(self):
          return self.meeting_name
  </code></pre>
  
  <p>I know the correct way to get a <code>list_display</code> for meetings in the <code>Visitors</code> admin panel is here: <a href="https://stackoverflow.com/a/18108586/2429989">https://stackoverflow.com/a/18108586/2429989</a>.</p>
  
  <p>However, how can I show a <code>list_display</code> for visitors at each meeting in the <strong><code>Meetings</code></strong> admin panel? I have tried:</p>
  
  <p>meetings/admin.py:</p>
  
  <pre><code>from django.contrib import admin
  from .models import Meeting
  from visitors.models import Visitor
  
  class MeetingAdmin(admin.ModelAdmin):
      list_display = ['id', 'team_member', 'show_visitors' ]
  
      def show_visitors(self, obj):
          return "\n".join([a.visitor_name for a in obj.visitor.all()])
  
  admin.site.register(Meeting, MeetingAdmin)
  </code></pre>
  
  <p>This results in <code>'Meeting' object has no attribute 'visitor'</code>, where am I going wrong?</p>