Answering myself, AFAICT I need to create migrations which look like the
following for every m2m intermediate table. The following assumes a "Book"
model which has a ManyToMany relationship to a "Tag" model:
from django.db import migrations
class Migration(migrations.Migration):
dependencies = [
("myapp", "0001_initial"),
]
operations = [
migrations.RunSQL(
[
'ALTER TABLE "myapp_book_tags" ALTER COLUMN "id" TYPE
bigint USING "id"::bigint',
'ALTER SEQUENCE "myapp_book_tags_id_seq" AS bigint',
],
elidable=True,
),
]
Kind regards,
Jeremy
On Monday, May 16, 2022 at 8:52:06 AM UTC+2 Jeremy Lainé wrote:
> Hi Mike,
>
> Thanks for the reply. For future reference, it was pointed out to me that
> I missed both an explicit note in the documentation [1] and an issue
> tracking a potential change in the future [2].
>
> Do you have any suggestions as to the actual SQL migration which needs to
> be applied for postgresql on each m2m table? Specifically, is it purely a
> matter of altering the "id" column type, or does something need to be done
> to the index?
>
> Cheers,
> Jeremy
>
> [1] https://docs.djangoproject.com/en/4.0/ref/settings/#default-auto-field
> [2] https://code.djangoproject.com/ticket/32674
>
> On Sunday, May 15, 2022 at 10:26:18 AM UTC+2 Mike Dewhirst wrote:
>
>> On 14/05/2022 11:44 pm, Jeremy Lainé wrote:
>>
>> Hi!
>>
>> I'm currently looking at how to migrate all my models from AutoField to
>> BigAutoField. For all the explicitly defined models the process seems
>> pretty straightforward:
>>
>> - change DEFAULT_AUTO_FIELD to BigAutoField
>> - generate migrations
>> - apply migrations
>>
>> However, when I inspect the database schema, I see that the
>> "intermediate" tables for many-to-many relations still have a primary key
>> of type "integer" (on postgresql). This means I'm no closer to avoiding
>> 32bit primary key exhaustion!
>>
>> Does anyone know how I can address this?
>>
>>
>> Not really.
>>
>> In my case I specify models for all my m2m intermediate tables as a
>> matter of course. It is how I think. In my schemas, most such tables
>> typically carry extra data about the relationships they define - therefore
>> I want models. The bigint migration obviously worked for me.
>>
>> Maybe you can use manage.py to write out your m2m models so you can
>> adjust then migrate them.
>>
>> settings.DEFAULT_AUTO_FIELD = "django.db.models.BigAutoField" should work
>> for new intermediate tables.
>>
>> Another option is to manually adjust all your m2m PostgreSQL id fields to
>> bigint.
>>
>> It is a lossless change and will never need to be reversed so it might be
>> easier to bite that bullet and move on.
>>
>> YMMV
>>
>>
>> Many thanks in advance,
>> Jeremy
>>
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