CODEWITHSUNDEEP
pythondjango
Jan
Jan

Reputation: 43169

Unknown IntegrityError in Django

I have this small project to create my bills through Django and Latex which worked flawlessly until today. Now when I try to add another costumer, Django throws

duplicate key value violates unique constraint "kunden_kundearbeitsamt_pkey"
DETAIL:  Key (id)=(4) already exists.

These are the model definitions in question:

class Kunde(models.Model):
    name = models.CharField('Name', max_length = 200)
    vorname = models.CharField('Vorname', max_length = 200)
    geburtsdatum = models.DateField('Geburtsdatum', max_length = 200)
    untersuchungsdatum = models.DateField('Untersuchungsdatum', max_length = 200)

    class Meta:
        abstract = True

class KundeArbeitsamt(Kunde):
    kundennummer = models.CharField('Kundennummer', max_length = 100)
    bglnummer = models.CharField('BGL-Nummer', max_length = 100)
    empfaenger = models.ForeignKey('rechnungen.NumberToEmpfaenger', blank = True, null = True)

    class Meta:
        verbose_name = "Proband Arbeitsamt"
        verbose_name_plural = "Proband Arbeitsamt"

    def __str__(self):
        return '{}, {}'.format(self.name, self.vorname)

The admin part where the object is created (nothing special, I guess):

from django.contrib import admin
from .models import KundeArbeitsamt

class KundeArbeitsamtAdmin(admin.ModelAdmin):
    ordering = ('name',)

admin.site.register(KundeArbeitsamt, KundeArbeitsamtAdmin)

I swear, I did not make any migrations or other changes to the database (Postgres) whatsoever. Django is handling the creation of the objects. What is causing this error and how to fix it?

Upvotes: 1

Views: 192

Answers (1)

dahrens
dahrens

Reputation: 3959

This error is raised by your database, because django wants to add an new column with an ID (=4) already in use.

To investigate further you need to find the part of your app responsible for creating the IDs. Django usually delegates this task to your database. In case of postgres the datatype serial is used. Postgres uses so called sequences for this purpose and generates and executes the following SQL for you:

CREATE SEQUENCE tablename_colname_seq;
CREATE TABLE tablename (
    colname integer NOT NULL DEFAULT nextval('tablename_colname_seq')
);
ALTER SEQUENCE tablename_colname_seq OWNED BY tablename.colname;

I would now start with checking the database sanity like that:

-- views contents of the table
SELECT * FROM kunden_kundearbeitsamt;
-- check the sequence
select currval('kunden_kundearbeitsamt_id_seq');

If the first shows 4 records with IDs 1, 2, 3 and 4 and the sequence answers with 4 everything is alright. I would proceed with the django sources to figure out why they pass an ID on object creating without relying on the sequence. The django shell might be a good place to start with in that case.

Otherwise I would fix the sequence and ask myself how this happend as it is barely the case that postgres makes mistakes at this point.

SELECT setval('kunden_kundearbeitsamt_id_seq', (SELECT max(id) FROM kunden_kundearbeitsamt));

Upvotes: 1

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