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From Francisco Peredo <franciscoper...@tabasco.gob.mx>
Subject Coming from EOF: Cayenne vs Hibernate
Date Wed, 11 Mar 2009 20:06:32 GMT

Hi!
My first contact with an ORM was EOF... an ever since I have felt that
nothing compares to it ;-).

The thing is, I have had to work with JPA/Hibernate for a few years now...
and I feel it has some weaknesses I really do not like, I am thinking about
"switching to cayenne" but first i would like to be sure that Cayenne does
not have this weaknesses too.

List of weaknesses in JPA/Hibernate:

-No way to manage an object that "will be persisted", in JPA/Hibernate if
you call entityManager.persist(object) and the database does not support
sequences (like MS-Sql) an insert will be triggered, and if any of the non
nullable fields of the objects is null, it will crash. If your object has a
compound primery key, things get worse, because the entityManager can not
deal with it until the compound primary key is set, and if you compound
primary key is formed by foreign keys pointing to objects that are new too,
that means you will not be able to save stuff with with a simple single call
to entityManager.persist to one of the objects, cascading will not help you
(I really miss something "magic" like ObjectContext.commitChanges() )

-No easy way to know if "an object is dirty" (if it has changed/deleted
since it was read from the database, there is just no API for that), and
since you can not know what objects will be persisted, and what object have
changed, and what objects will be deleted from database, that means you can
not easily create an unified API for centralized polymorphic validation
(that is no easy way to create validateForSave, or validateForDelete)

-No real equivalent for validateForXXX, JPA lifecycle callbacks are not
match for validateForXXX because you can not query the database during the
lifecycle callbacks, and if you throw an exception inside a lifecycle
callback, the JPA/Hibernate entityManager enters an invalid state, and after
that you can not continue to use your POJOs, you have to start over with a
fresh entityManager... and without you modifications to the POJOs. Note that
Hibernate new validation framework does not offer a real solution for this
problem... and AFAIK JSR-000303 will not help with this either.

-No support for some kind of temporary id: In JPA/Hibernate, the id for an
object is "null" until you flush it to the database, so if you need to
reference a particular object instance from the user interface... there is
plain no way to do it, you have to "save it first" to get a primary key.

Those are my main disagreements with the way I have to work with
JPA/Hibernate... will switching to 
Cayenne help me with those? And if it works... here is a crazy idea... what
if you guys developed a wrapper that could work on top of any JPA provider
to offer a higher level EOF like API ?

Regards,
Francisco

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