Fixed #373 -- Added CompositeField-based Meta.primary_key.

[csirmazbendeguz]

Trac ticket number

ticket-373

Branch description

This branch is based on PR #17279.
See my proposal.

Code example:

class Tenant(models.Model):
    pass


class User(models.Model):
    tenant = models.ForeignKey(Tenant, on_delete=models.CASCADE)
    id = models.SmallAutoField()

    class Meta:
        primary_key = ("tenant_id", "id")


class Comment(models.Model):
    tenant = models.ForeignKey(Tenant, on_delete=models.CASCADE)
    id = models.SmallAutoField()
    user_id = models.SmallIntegerField()
    user = models.ForeignObject(
        User,
        on_delete=models.CASCADE,
        from_fields=("tenant_id", "user_id"),
        to_fields=("tenant_id", "id"),
        related_name="+",
    )

    class Meta:
        primary_key = ("tenant_id", "id")

[csirmazbendeguz]

@charettes, could you give it a look? It looks like a big PR, but most of the changes are just tests.

[csirmazbendeguz]

I squashed all the commits in a new PR, so closing this (it was easier to open a new PR than to resolve all the conflicts).