On Mar 11, 2009, at 3/113:06 PM , Francisco Peredo wrote:
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() )
I routinely: objectContext.newObject(Foo.class);
or:
objectContext.registerNewObject(foo);
with objects that have required fields, etc. Cayenne will mark this as
an object in state "NEW" (as opposed to transient, which is an
unmanaged object).
I've had no issues with compound primary keys which are also FK's.
(make sure toDepPK is checked on the proper side of teh relationship
in the modeler).
-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)
Sure. You can query the object context for all modified objects.
You can also directly check the state of an object (MODIFIED, NEW,
COMMITTED, DELETED, TRANSIENT).
Of those, only COMMITTED implies that an object is managed, stored in
the db, and unmodified since it's fetch.
I've used this to do things like implementing object "histories"
stored to the db.
-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.
validateForXXX is supported, including querying into the database.
I have an app that has an "Enrollment" object with a start and end date.
One of the business rules is that no two enrollments for a given user
should overlap.
So when the object is saved (update or insert), I query the db for
existing enrollments, and add a validation violation
-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.
Yup; definitely an annoyance in hibernate/JPA. Fortunately, cayenne
objects that are in state NEW /do/ have a temporary id.
the tapestry5/cayenne integration module takes advantage of this fact
to do exactly what you mention (referencing a particular object in the
UI, even if it's new).
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 ?
Heh. That's an interesting idea. Seems like we have our hands full
just developing the core cayenne framework at the moment, though....
patches always welcome, of course. ;)
Robert
Regards,
Francisco
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