#35763: Setting the auto increment value of a database model breaks when you
add a
new field to the model
-------------------------------------+-------------------------------------
Reporter: Kevin Renskers | Type: Bug
Status: new | Component: Database
| layer (models, ORM)
Version: 5.1 | Severity: Normal
Keywords: | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Setting the auto increment value of a database model breaks when you add a
new field to the model. It only breaks in SQLite.
I have simple model `Content`:
{{{
class Content(models.Model):
name = models.CharField(max_length=255, blank=True)
}}}
In the initial migration I've added an extra operation:
{{{
migrations.RunSQL("INSERT INTO sqlite_sequence (seq, name) VALUES (50000,
'content_content');"),
}}}
Now when I create my first model instance its ID starts at 50,001, as
expected. However when I then add a second field to my `Content` model and
create a migration, now my first model instance ID is 1 instead of 50,001.
Somehow the `migrations.AddField` operation has undone the
`sqlite_sequence` modification.
I have a repro here: https://github.com/kevinrenskers/django-seq-repro.
It has two commits:
1. The initial commit where a `Content` model is added, and in the initial
migration I set the initial auto increment value. A test is added to make
sure the first model instance has ID 50,001, which passes.
2. The second commit adds a single field to the `Content` model (with the
accompanying migration file), and now the test fails.
The test can be fixed by adding another `RunSQL` command to the second
migration:
`migrations.RunSQL("UPDATE sqlite_sequence SET seq = 50000 WHERE name =
'content_content'"),`
It seems like a bug that the auto increment modification is undone by the
second migration.
Important to note: this only happens in SQLite. With PostgreSQL the query
in the initial migration would be `ALTER SEQUENCE content_content_id_seq
RESTART WITH 50000;`, and the test still passes after adding the new field
to the `Content` model. Only with SQLite does it break and is the second
operation to update `sqlite_sequence` necessary.
--
Ticket URL: <https://code.djangoproject.com/ticket/35763>
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