Django Many-To-One IntegrityError

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I am new to Python and Django. I created database due to documents. I tested it and there has been error to many-to-one relationship between two models.

It looks weird to me because It works like one to one relationship between those classes but it gives error if I try to add many. There are other classes with same relationship as many-to-one. I created same way and they work just fine. I am using sqlite by the way.

class unites (models.Model):
    id = models.IntegerField(primary_key=True)
    unitename = models.CharField(max_length=128)


class intensivecare_forms (models.Model):
    id = models.IntegerField(primary_key=True)
    hospitals_id = models.ForeignKey(hospitals, on_delete=models.CASCADE)
    formname = models.CharField(max_length=128)
    data = models.JSONField()
    unites_id = models.ForeignKey(unites, on_delete=models.CASCADE)

It gives this error if I try to add second form into unites.

IntegrityError at /admin/LocalManager/intensivecare_forms/add/

UNIQUE constraint failed: LocalManager_intensivecare_forms.unites_id_id

Request Method:     POST
Request URL:    http://localhost:8000/admin/LocalManager/intensivecare_forms/add/
Django Version:     3.2.4
Exception Type:     IntegrityError
Exception Value:    

UNIQUE constraint failed: LocalManager_intensivecare_forms.unites_id_id

Exception Location:     /Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/site-packages/django/db/backends/sqlite3/base.py, line 423, in execute
Python Executable:  /Library/Frameworks/Python.framework/Versions/3.9/bin/python3
Python Version:     3.9.6
many-to-one django-orm django-models django
1 Answers

The unites_id was a OneToOneField initially. A OneToOneField is basically a ForeignKey with unique=True, such that two intensivecare_forms can not point to the same unites.

Later you turned it into a ForeignKey, but forgot to migrate the database, so the UNIQUE constraint was still enforced by the database.

By makemigrations and migrate, normally you can drop the UNIQUE constraint, and thus let two intensivecare_forms point to the same unites.

user_675790
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