#30969: Add support for query expressions as default values
-------------------------------------+-------------------------------------
Reporter: Johannes Hoppe | Owner: nobody
Type: Uncategorized | Status: new
Component: Database layer | Version: master
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage:
| Unreviewed
Has patch: 1 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
-------------------------------------+-------------------------------------
Changes (by Johannes Hoppe):
* has_patch: 0 => 1
Old description:
> Add support for query expressions – like `Now()` – as default values of
> model fields.
>
> e.g.
>
> {{{
> class MyModel(models.Model):
> created = models.DateTimeField(default=models.Now())
> }}}
>
> This was originally part of my patch for
> [#29444](https://code.djangoproject.com/ticket/29444), but I deferred it
> to keep the changeset more moderate.
>
> There are a couple things here to consider:
>
> 1. This feature will only be supported in PostgreSQL and Oracle. Other
> Databases do allow setting defaults, but can not return them on insert.
>
> 2. Since the default is provided by the database, fields with a query
> expression as a default should default not to be editable. This will
> avoid confusion in interfaces like, Django admin, since these fields will
> be empty upon insert and then magically have a value. This is behavior
> would be consistent with the auto increment fields.
>
> Since I extracted this from another feature branch, the patch is already
> done. I will link it, as it might help to understand the proposal a bit
> better.
> This is the current patch:
> https://github.com/django/django/pull/11783
New description:
Add support for query expressions – like `Now()` – as default values of
model fields.
e.g.
{{{
class MyModel(models.Model):
created = models.DateTimeField(default=models.Now())
}}}
This was originally part of my patch for
[https://code.djangoproject.com/ticket/29444], but I deferred it to keep
the changeset more moderate.
There are a couple things here to consider:
1. This feature will only be supported in PostgreSQL and Oracle. Other
Databases do allow setting defaults, but can not return them on insert.
2. Since the default is provided by the database, fields with a query
expression as a default should default not to be editable. This will avoid
confusion in interfaces like, Django admin, since these fields will be
empty upon insert and then magically have a value. This is behavior would
be consistent with the auto increment fields.
Since I extracted this from another feature branch, the patch is already
done. I will link it, as it might help to understand the proposal a bit
better.
This is the current patch:
https://github.com/django/django/pull/11783
--
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Ticket URL: <https://code.djangoproject.com/ticket/30969#comment:1>
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