django.db.utils.IntegrityError: duplicate key value violates unique constraint “django_content_type_pkey”

Question

Ran into a bit of a problem, i\'m getting the above error message when i run \'python manage.py syncdb\' I\'m working on a fairly old site. It\' running django

Answer 1

I received this error:

django.db.utils.IntegrityError: duplicate key value violates unique constraint 
    "blahmodule_blahthing_blahstuff_id"
DETAIL:  Key (blahstuff_id)=(1) already exists.

A possible solution:

• Try migrating the blahstuff relation in blahthing from a OneToOneField field to a ForeignKey

An explanation with what I was using:

I was using the Django RestFramework which was wired up through a ListCreateAPIView, and a ModelSerializer. For whatever reason the OneToOneField attaches a UNIQUE to one of the join tables blahmodule_blahthing_blahstuff_id, ( i'm not actually sure if its a join table, this is an assumption ), but whatever magic is happening in django switching to a ForeignKey with QuerySet returns, solved my issue.

related:

• What's the difference between django OneToOneField and ForeignKey?
• https://www.postgresql.org/docs/11/ddl-constraints.html

As far as the actual question above:

schema :

-- Table: public.django_content_type

-- DROP TABLE public.django_content_type;

CREATE TABLE public.django_content_type
(
    id integer NOT NULL DEFAULT nextval('django_content_type_id_seq'::regclass),
    app_label character varying(100) COLLATE pg_catalog."default" NOT NULL,
    model character varying(100) COLLATE pg_catalog."default" NOT NULL,
    CONSTRAINT django_content_type_pkey PRIMARY KEY (id),
    CONSTRAINT django_content_type_app_label_model_76bd3d3b_uniq UNIQUE (app_label, model)

)
WITH (
    OIDS = FALSE
)
TABLESPACE pg_default;

ALTER TABLE public.django_content_type
    OWNER to YOURUSER;

Example rows:

pk    app_label                model

1   "your_app"           "your_app_model"
2   "your_app"           "your_app_model"
3   "blah_module"        "blahthing"
4   "blah_module"        "blahstuff"

The hash on django_content_type_app_label_model_76bd3d3b_uniq and the Primary Keys can get jumbled up if a migration fails mid process.