conflict between OneToMany and OneToOne relationship in Django

Question

I need to define a Meeting model which includes an organiser and a number of participants. All participants are derived from the standard User in auth module.

from django.db import models
from django.contrib.auth.models import User

class Meeting(models.Model):
    organizer=models.ForeignKey(User)
    participants=models.ManyToManyField(User)

However, when running syncdb, the I got the following error

Error: One or more models did not validate: hub.meeting: Accessor for field 'organizer' clashes with related m2m field 'User.meeting_set'. Add a related_name argument to the definition for 'organizer'. hub.meeting: Accessor for m2m field 'participants' clashes with related field 'User.meeting_set'. Add a related_name argument to the definition for 'participants'.

Can anyone help me to solve this?

The title of this question doesn't have anything to do with the problem: I would suggest changing it — Timmy O'Mahony, Nov 06 '11 at 17:08

score 3 · Accepted Answer · edited May 23 '17 at 12:21

class Meeting(models.Model):
    organizer=models.ForeignKey(User, related_name="meetings_orginizer")
    participants=models.ManyToManyField(User, related_name="meetings_participants")

If you have a user object and you want to follow the relationship backwards to find either the meetings that user is an organizer of or meetings that the user is a participant of, you need to specifically name a 'related_name' field on the model to distinguish them. Now you can follow the relationship backwards like so:

me = User.objects.get(id=0)
# Meetings I'm organising
m1 = me.meetings_orginizer.all()
# Meetings I'm participating in
m2 = me.meetings_participants.all()

score 1 · Answer 2 · answered Nov 06 '11 at 17:02

the problem (as stated by the error message) has to do with backwards relations. when you define a foreign key (or many2many), django sets up a reverse relation User.meeting_set. however, since you have two relations, the reverse relations clash and you have to specify the related names manually. see the docs here and here

code as in answer above

conflict between OneToMany and OneToOne relationship in Django

2 Answers2