UUIDs Have 36 Characters Not 32

[kylie-sre]

Subject: The mapping for a Django UUIDField to a Redshift field is varchar(32). UUID's have 36 characters including the dashes.

Problem

• There is a length mismatch for UUIDFields

Procedure to reproduce the problem

• Create a model and add a UUIDField
• Generate and apply a migration
• Attempt to insert a UUID in to the resulting table without using the Django model (we are using kinesis to do writes and using this package to manage redshift schemas)

Error logs / results

When using the folowing query to get the error from redshift

SELECT error_message, column_name, start_time, * FROM sys_load_error_detail ORDER BY start_time DESC;

the following error is returned

String length exceeds DDL length

Expected results

the migration results in a usable field

[shimizukawa]

Actually, django's UUIDField is implemented as a varchar(32).
https://github.com/django/django/blob/c5d196a65264136ee6795356871a29f3d22ec52f/django/db/models/fields/__init__.py#L2658-L2660

For this reason, I think it is natural that django-redshift-backend also implements UUIDs as 32-character strings.

However, python's uuid.UUID(hex=value) can restore UUID values with a 36-character string including hyphens.
Considering that Redshift is used in conjunction with other systems on AWS, I think it is more flexible to be able to handle 36 characters, so I think it is reasonable to support it.

https://github.com/django/django/blob/c5d196a65264136ee6795356871a29f3d22ec52f/django/db/models/fields/__init__.py#L2684-L2688

$ python
Python 3.10.14 (main, May 14 2024, 08:39:53) [GCC 12.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import uuid
>>> u = uuid.uuid4()
>>> u
UUID('993376e9-2ee7-4f29-8578-4fa38f889b8d')
>>> str(u)
'993376e9-2ee7-4f29-8578-4fa38f889b8d'
>>> len(str(u))
36
>>> str(u.hex)
'993376e92ee74f2985784fa38f889b8d'
>>> len(str(u.hex))
32
>>> uuid.UUID(hex=str(u))
UUID('993376e9-2ee7-4f29-8578-4fa38f889b8d')
>>> uuid.UUID(hex=str(u.hex))
UUID('993376e9-2ee7-4f29-8578-4fa38f889b8d')

[shimizukawa]

This issue was implemented in PR #138.
Thanks for your contribution.