The java.util.Set collection type is supposed to ensure that objects in
the collection are unique. (In EJB 2.0 uniqueness in a Set is based on
the entitys' primary keys. ) However, the specification doesn't require
that the container enforce uniqueness. So, for example, as a bean
developer I might specify Set as the cmr-field-type, but the underling
EJB container and database may not actually enforce this.
Section 10.3.6.2 states "The semantics of a set accessor method, when
applied to a collection-valued cmr-field, is also determined by the
referential integrity semantics associated with the multiplicity of the
relationship." This would seem to imply that it's not entirely the
container's responsibility to enforce the uniqueness constraint on Set
cmr fields. In fact, EJB vendors may choose not to enforce it at all,
leaving it in the hands of the database and the referential integrity
defined for that data.
I'm wondering what vendors think about this. Obviously, Section 10.3.6.2
has a variety of implications, which are important to all relationship
fields -- but lets keep this thread a least focused on the use of Set.
Thanks,
Richard
--
Richard Monson-Haefel
Author of Enterprise JavaBeans, 2nd Edition (O'Reilly 2000)
Co-Author of Java Message Service (O'Reilly 2000)
http://www.jMiddleware.com
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