#35956: Add composite foreign keys
-------------------------------------+-------------------------------------
Reporter: Csirmaz Bendegúz | Owner: (none)
Type: New feature | Status: new
Component: Database layer | Version: dev
(models, ORM) |
Severity: Normal | Resolution:
Keywords: | Triage Stage: Accepted
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Clifford Gama):
Replying to [comment:4 Csirmaz Bendegúz]:
> Replying to [comment:2 Mariusz Felisiak]:
> > Do we need these parameters? `CompositePrimaryKey` is always a primary
key so its fields should be detected automatically, IMO, the following
example should work:
> > {{{#!python
> > class Release(models.Model):
> > pk = models.CompositePrimaryKey("version", "name")
> > version = models.IntegerField()
> > name = models.CharField(max_length=20)
> >
> >
> > class RefRelease(models.Model):
> > release = models.ForeignKey("Release", models.CASCADE)
> > }}}
>
> The issue with this example is `RefRelease` must have 2 fields matching
the `CompositePrimaryKey` (an `IntegerField()` and a
`CharField(max_length=20)`).
>
> So `release` would need to create 2 fields ''implicitly'' and I think
that's too restrictive.
>
> We should allow **sharing fields between composite foreign keys**.
I'm +1 on sharing fields, but I think that Felix's suggestion should work
as the default.
In simple cases, having the foreign key automatically infer and create the
needed fields is great developer experience — it keeps things intuitive
and close to how `ForeignKey` works today.
That said, we should definitely allow shared fields. For example, if a
model already has a `tenant_id` FK to `Tenant`, and also needs to
reference a model with a composite PK like `(tenant_id, id)`, it should be
able to reuse the same `tenant_id` field in both relationships.
So if possible, maybe we should have implicit field creation as default,
and `to|from_fields` as an opt-in for more advanced use cases
--
Ticket URL: <https://code.djangoproject.com/ticket/35956#comment:7>
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