[hibernate-issues] [Hibernate-JIRA] Commented: (ANN-140) Discriminator column not supported with JOINED strategy

[Amit Kasher (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/ANN-140?page=comments#action_26196 ] 

Amit Kasher commented on ANN-140:
---------------------------------

I'd like to add another possible requirement for discriminator column support. If you have a discriminator column, you can have it inside DB constraints, and achieve constraints in which subclasses participate as different entities.

Example: I have the following entities:

A {
id, name
}

B extends A {
height
}

C extends A {
width
}

I need the following constraint: I don't want to allow (more than 1:) 2 or more instances of B with the same name, and I don't want (more than 1:) 2 or more instances of C with the same name. However, I DO want to allow 1 instance of B with the name "Jack", and another instance, this time of C, with that same name, "Jack". The only way to achieve this, I think, is having a discriminator column in A which will allow you to define a unique constraint containing A.discriminator and A.name.

> Discriminator column not supported with JOINED strategy
> -------------------------------------------------------
>
>          Key: ANN-140
>          URL: http://opensource.atlassian.com/projects/hibernate/browse/ANN-140
>      Project: Hibernate Annotations
>         Type: Bug

>     Versions: 3.1beta6
>  Environment: Hibernate 3.1rc2, Hibernate Annotations 3.1b6
>     Reporter: Steven Grimm

>
>
> Section 9.1.27 of the EJB3 persistence public draft says, "The DiscriminatorColumn annotation is used to define the discriminator column for SINGLE_TABLE and JOINED mapping strategies." But Hibernate ignores the DiscriminatorColumn annotation when the mapping strategy is JOINED; when a JOINED entity is persisted, its discriminator column is not included in the SQL "insert" statement, resulting in a not-null constraint violation if the discriminator column is marked NOT NULL in the database.
> The JOINED strategy with discriminators is pretty ubiquitous in EJB3 sample code and tutorials out on the net, so lots of people are likely to run into this as they try out EJB3 for the first time. A few examples:
> http://www.oracle.com/technology/tech/java/oc4j/ejb3/howtos-ejb3/howtoejb30inheritance/doc/how-to-ejb30-inheritance.html
> http://www.solarmetric.com/Software/Documentation/4.0.0EA/docs/full/html/ejb3_overview_mapping_discrim.html
> http://www.caucho.com/resin-3.0/amber/tutorial/cmp-inherit/index.xtp

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