I'd be interested in seeing this. Generated columns are a useful SQL
feature that are missing from Django.
Nice initial research on backend coverage - it looks like they're widely
supported.
Some ideas...
Is it necessary to take a base field? Can we not determine the output field
type for some kinds of expression? e.g. F("some_integer_field") + 1 can be
assumed to have output field type IntegerField.
Would it be worth blocking assignment to the field? Allowing
"model.generated_field = ..." would at least be misleading. (This could be
done with a special descriptor.)
Good luck!
On Wed, Apr 13, 2022 at 11:25 AM Paolo Melchiorre <pa...@melchiorre.org>
wrote:
> Hi all,
>
> I am at PyCon DE 2022 in Berlin with Markus and I shared with him this
> idea that I have been thinking about for a few months, given his
> interest I also share it with you.
>
> I figured we could add in Django a "GeneratedField" which accepts a
> "base_field" attribute in a similar way to "ArrayField" and then an
> expression to generate a value for the field.
>
> For example this model:
>
> class Album(models.Model):
> ...
> title = models.CharField(max_length=120)
> search = GeneratedField(
> SearchVectorField(),
> F('title')
> )
>
> would generate an SQL code like this in PostgreSQL:
>
> CREATE TABLE album (
> ...
> title char(120),
> search tsvector GENERATED ALWAYS AS title STORED
> );
>
> I found some documentation for different database backend about
> generated column (or similar names)
>
> # SQLite
> https://www.sqlite.org/gencol.html
> https://www.sqlite.org/releaselog/3_31_0.html
>
> # PostgreSQL
> https://www.postgresql.org/docs/12/ddl-generated-columns.html
> https://www.postgresql.org/docs/12/release-12.html
>
> # Oracle
> https://oracle-base.com/articles/11g/virtual-columns-11gr1
>
> # MySQL
> https://dev.mysql.com/doc/refman/5.7/en/mysql-nutshell.html
> https://dev.mysql.com/doc/refman/5.7/en/create-table-generated-columns.html
>
> # MariaDB
> https://mariadb.com/kb/en/changes-improvements-in-mariadb-102/
> https://mariadb.com/kb/en/generated-columns/
>
> I'd love to hear your thoughts on this idea and if you think it might
> be something worth continuing to investigate.
>
> Greetings from PyCon DE 2022 in Berlin,
> Paolo
>
> --
> https://www.paulox.net
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