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From "Jeremy Bauer (JIRA)" <j...@apache.org>
Subject [jira] Created: (OPENJPA-670) Discriminator column is missing from table when inheritance is used without annotation
Date Tue, 29 Jul 2008 21:07:31 GMT
Discriminator column is missing from table when inheritance is used without annotation
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                 Key: OPENJPA-670
                 URL: https://issues.apache.org/jira/browse/OPENJPA-670
             Project: OpenJPA
          Issue Type: Bug
          Components: jdbc
    Affects Versions: 1.2.0, 1.3.0
            Reporter: Jeremy Bauer


According to the EJB 3.0 JPA spec (pp. 191, section 9.1.29):

"If the Inheritance annotation is not specified or if no inheritance type is specified for
an entity class
hierarchy, the SINGLE_TABLE mapping strategy is used."

I've found that if an entity inheritance hierarchy is specified without an explicit DiscriminatorColumn
or Inheritance annotation, a single table will be used for mapping, but there will be no discriminator
column in the table.  

pp. 191 - 192, section 9.1.30 of the spec reads:

"For the SINGLE_TABLE mapping strategy, and typically also for the JOINED strategy, the persistence
provider will use a type discriminator column."

and

"If the DiscriminatorColumn annotation is missing, and a discriminator column is required,
the
name of the discriminator column defaults to "DTYPE" and the discriminator type to STRING."

Without a discriminator column a scenario such as:

entity B extends entity A
entity C extends entity A

"select c from C"  will return entities of type A, B, and C (which is a data integrity issue)
because there is no way to distinguish between the entity types.

The simple workaround is to specify an @Inheritance or @DiscriminatorColumn annotation on
the root class, but OpenJPA should exhibit default behavior defined by the spec when these
annotations are not specified.

I have a patch and jUnits in the works and will post them shortly.


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