Support for multi tenancy column discriminator

[guitcastro]

Description

#5681 added support to hibernate, however the column discriminator was not supported, because by the time, Hibernate itself didn't have fully support for it.

        if (multiTenancyStrategy == MultiTenancyStrategy.DISCRIMINATOR) {
            // See https://hibernate.atlassian.net/browse/HHH-6054
            throw new ConfigurationException("The Hibernate ORM multitenancy strategy "
                    + MultiTenancyStrategy.DISCRIMINATOR + " is currently not supported");
        }

However, HHH-6054 is now completed and we can have support for discriminator column.

Implementation ideas

No response

[quarkus-bot]

/cc @Sanne, @gsmet, @yrodiere

[yrodiere]

To clarify context: HHH-6054 is only fixed in Hibernate ORM 6, and Steve has stated pretty clearly it won't be backported to Hibernate ORM 5.

Quarkus (as much of the Java ecosystem, unfortunately) is still on ORM 5, because ORM 5 uses older Java EE packages (javax.persistence.*) while ORM 6 uses Jakarta EE packages (jakarta.persistence.*), so upgrading is a rather intrusive change.

Thus, support for discriminator-based multi-tenancy will happen, but only in Quarkus 3, which will upgrade to Hibernate ORM 6.

[guitcastro]

Linking 26986 for reference.

[humcqc]

Linking 32686 for reference, WIP.

[yrodiere]

Fixed by #32855