Multiple 'self' referencing ManyToManyFields in one model overwrite each other's data
|Reported by:||notanumber||Owned by:||nobody|
|Component:||Database layer (models, ORM)||Version:||master|
|Severity:||Keywords:||ManyToManyField, self, multiple|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
Defining multiple ManyToManyFields in one model is problematic. When updating one field, all of the others are updated with the same data.
For example, in the following model:
from django.db import models class Job(models.Model): title = models.CharField(max_length=100) reports_to = models.ManyToManyField('self', null=True, blank=True, related_name='reports_to_set') supervises = models.ManyToManyField('self', null=True, blank=True, related_name='supervises_set') class Admin: pass def __unicode__(self): return self.title
Updating a user's data, "Bill", 'reports_to' to read "John", also sets 'supervises' to "John" as well. Obviously, in this case at least, this is not the desired behaviour.
Adding symmetrical=False does not correct this issue, but raises another: When updating "Bill" to 'reports_to' "John", we end up with both users having "John" & "Bill" in their 'reports_to' & 'supervises' fields.
Tested this on WindowsXP, using SQLite3 & the built-in 'runserver' command.
The test application & project is attached to this ticket. The admin user/password is "test"/"test123"