id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
32869	Bug while migrating a OneToOneField to ForeignKey on PostgreSQL.	suhail vs	nobody	"Using PostgreSQL Database I changed a field from `OneToOneField` to `ForeignKey`::

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

# Create your models here.
class Customer(models.Model):
    user = models.OneToOneField(User, on_delete=models.CASCADE, null=True) 
}}}

to 

{{{
class Customer(models.Model):
    user = models.ForeignKey(User, on_delete=models.CASCADE, null=True) 
}}}

after migrations, then i tried to create a Customer i got error: 

{{{
IntegrityError at /admin/myapp/customer/add/
duplicate key value violates unique constraint ""myapp_customer_user_id_key""
DETAIL:  Key (user_id)=(1) already exists.
Request Method:	POST
Request URL:	http://localhost:8001/admin/myapp/customer/add/
Django Version:	3.2.4
Exception Type:	IntegrityError
Exception Value:	
duplicate key value violates unique constraint ""myapp_customer_user_id_key""
DETAIL:  Key (user_id)=(1) already exists.
Exception Location:	/home/donams/suhail/github/temp/test_unique/env/lib/python3.6/site-packages/django/db/backends/utils.py, line 84, in _execute
Python Executable:	/home/donams/suhail/github/temp/test_unique/env/bin/python
Python Version:	3.6.9
Python Path:	
['/home/donams/suhail/github/temp/test_unique',
 '/usr/lib/python36.zip',
 '/usr/lib/python3.6',
 '/usr/lib/python3.6/lib-dynload',
 '/home/donams/suhail/github/temp/test_unique/env/lib/python3.6/site-packages']
Server time:	Mon, 21 Jun 2021 11:22:55 +0000
}}}"	Bug	closed	Migrations	3.2	Normal	worksforme	postgres onetoonefield foreignkey		Unreviewed	0	0	0	0	0	0