Postgres Sequences as Default Value for Django Model Field

Question

I have a PostgreSQL database that is being used by a front-end application built with Django, but being populated by a scraping tool in Node.js. I have made a sequence that I want to use across two different tables/entities, which can be accessed by a function (nexval(serial)) and is called on every insert. This is not the primary key for these tables, but simply a way to maintain order through some metadata. Using it in Node.js during the insertion of the data into the tables is trivial, as I am using raw SQL queries. However, I am struggling with how to represent this using Django models. There does not seem to be any way to associate this Postgres function with a model's field.

Question: Is there a way to use a Postgres function as the default value of a Django model field?

you can create a custom database type, and a custom field

alfonso.kim
– alfonso.kim

2017-06-09 13:41:32 +00:00
Commented Jun 9, 2017 at 13:41 — alfonso.kim
– alfonso.kim, Commented Jun 9, 2017 at 13:41

MrE · Accepted Answer · 2018-11-01 16:32:25Z

3

you can also set your own function for the default

from django.db import connection, models

def sequence_id():
  with connection.cursor() as cursor:
    cursor.execute("""SELECT nextval('model_someid_seq')""")
    return cursor.fetchone()[0]


class MyModel(models.Model):
  field_id = models.IntegerField(default=sequence_id)

answered Nov 1, 2018 at 16:32

MrE

21.1k15 gold badges92 silver badges113 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

user3486626 Over a year ago

If i do this the sequence runs many times. Easy 30 times. I use your function "sequence_id()" in admin.py overriding save_model

P Ackerman · Accepted Answer · 2017-06-28 14:55:34Z

1

My eventual solution:

Override the save method of the model, using a raw query to SELECT nextval('serial') inside the override, setting that as the value of the necessary field, then call save on the parent (super(PARENT, self).save()).

answered Jun 28, 2017 at 14:55

P Ackerman

2,43423 silver badges25 bronze badges

Collectives™ on Stack Overflow

Postgres Sequences as Default Value for Django Model Field

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related