On Jan 22, 2007, at 2:48 PM, Aristedes Maniatis wrote:
On 22/01/2007, at 10:47 PM, Andrus Adamchik (JIRA) wrote:
JPA specification supports a notion of "embeddable" class.
Embeddable classes can be viewed as multi-column custom types that
do not have their own identity and belong to another persistent
object. Entities that embed them can override DB column mapping.
Currently Cayenne supports single-column custom types via
ExtendedType mechanism. We need to expand that to support multi-
column Embeddables and mapping via the Modeler.
When would you use such a thing? I am trying to think of how this
is useful, but perhaps I'm missing the point of the concept. Would
this be used to create a type of inheritance between classes, such
as company and person having a common billing address class but
relating back to completely separate address fields in each of the
company and person tables in the db?
Indeed IMO this is somewhat of an optional edge case in ORM (although
the JPA spec does require it). It adds extra flexibility to the
object design, allowing to map a composition of objects to a single
table. I think your inheritance example is a good one - you can have
the same Java class with specific OO behavior (e.g. Address) shared
across different entities and mapped to different columns.
Also, is it a goal to make 3.0 fully JPA compliant or is that too
ambitious in the timeframe (I'm guessing a reasonable target for
3.0 would be some time in 6-9 months).
Yes - the goal is to make 3.0 fully compliant. Although I'd postpone
the final decision till we finally start in-container integration
testing and running against the Sun TCK. In any event the plan is to
start posting 3.0 milestone releases ASAP.
Andrus
