#35731: Fields with db_default, and without default, are initialized to
instance of
DatabaseDefault
-------------------------------------+-------------------------------------
Reporter: kylebebak | Type:
| Cleanup/optimization
Status: new | Component: Database
| layer (models, ORM)
Version: 5.0 | 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
-------------------------------------+-------------------------------------
For example, if client code creates a model `Foo` with `val =
IntegerField(db_default=10)`, does `foo = Foo()`, and accesses `foo.val`,
they get an instance of `django.db.models.expressions.DatabaseDefault`.
This `DatabaseDefault` seems to be used for bookkeeping until the model
instance is written to the DB, after which `foo.val` is an `int`. IMO this
is not a good design, because it's a case of an implementation detail
(setting a value for the field once it's saved to the DB) changing the
model's public interface (IMO a model instance's field values are part of
its public interface).
If instead we do `val = IntegerField()`, and `foo = Foo()`, and access
`foo.val`, we get `None`, s.t. the type of `foo.val` is `int | None`.
Using `db_default` means that the type of `foo.val` is now `int |
DatabaseDefault`. `DatabaseDefault` is a bookkeeping type that client code
usually shouldn't interact with. If users aren't aware of `db_default`'s
implementation, they might still write code like this, which would be
broken: `if foo.val is not None: print(foo.val + 10)`.
Because `DatabaseDefault` is for bookkeeping, it seems like there's no
reason the model instance couldn't store its `DatabaseDefault` instances
on a "private" field which wouldn't affect the model's public interface.
This would be a lot cleaner IMO. Most users shouldn't know about
`DatabaseDefault`, which unsurprisingly isn't mentioned here,
https://docs.djangoproject.com/en/5.1/ref/models/fields/#db-default, or
anywhere else in the docs AFAICT.
--
Ticket URL: <https://code.djangoproject.com/ticket/35731>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/01070191bf6af9a2-1fe4918b-d1ce-4b6b-95a0-037d549e94e1-000000%40eu-central-1.amazonses.com.
