List_display for ManytoMany fields in Admin panel

Question

I have 2 apps: Visitors and Meetings, linked via a ManytoMany field:

visitors/models.py:

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

meetings/models.py:

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

I know the correct way to get a list_display for meetings in the Visitors admin panel is here: https://stackoverflow.com/a/18108586/2429989.

However, how can I show a list_display for visitors at each meeting in the Meetings admin panel? I have tried:

meetings/admin.py:

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)

This results in 'Meeting' object has no attribute 'visitor', where am I going wrong?

Answer 1

The default reverse lookup relation it's always obj.tablename_set. In your case you need to use obj.visitor_set.all()

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_set.all()])

However, you can customize the name of the reverse lookup by defining the related_name:

class Visitor(models.Model):
    visitor_name = models.CharField(default='name', max_length=128, blank=False, null=False)
    visitor_meetings = models.ManyToManyField(Meeting, related_name='visitors')

    def __str__(self):
        return self.visitor_name

All Meeting objects will now have access to visitors. Use it like:

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.visitors.all()])