Hi Marcin
Multiple column primary keys is a long-open feature request. There's a wiki
page: https://code.djangoproject.com/wiki/MultipleColumnPrimaryKeys and the
ticket, still open, is #373: https://code.djangoproject.com/ticket/373 .
I'm not sure your suggestion of removing the ".pk" mapping will either be
easy ("pk" is used a LOT throughout the ORM, not just for foreign keys), or
really help you very much (how would insertions really work, etc.)
I've thought of a technique before for making composite PK's work, though
haven't tested it. It should be possible to put a database view in front of
your table that combines your primary key columns into one string. For
example:
CREATE VIEW book_view AS SELECT CONCAT(catalogue_id, '-', book_id) AS
primary_key, author_id, ... FROM book;
Then define your model as having a CharField as a primary key. PostgreSQL
and MariaDB/MySQL will both automatically make single-table views map
inserts and updates to the underlying table. Though you might need a
trigger to allow inserts (new object saves) to work, splitting the parts
back out.
If you try this, let me know.
Thanks,
Adam
On Wed, 1 Apr 2020 at 11:34, Marcin Nowak <marcin.j.no...@gmail.com> wrote:
> Hi.
>
> I'd ask about "models.E026: The model cannot have more than one field
> with primary_key=True".
> It's not a true. The table or view *can* have more than one *column* as a
> part of a primary key.
> It's pretty common, when you have views with cross joins or unpivots.
>
> I can add models.E026 to silenced system checks, but Django is mapping PK
> to the first field of the complex primary keys. This can introduce some
> issues.
>
> I know that supporting complex PKs is hard and generally unsupported, but
> how about removing auto-mapping ".pk" attribute for models with complex
> primary key
> As a result there will be no possibility to declare foreign keys to such
> models, but there will be possibility to change E026to W0nn (just a
> warning).
>
> Regards,
> Marcin
>
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