> Hello,
>
> I've been trying to convert one of our
> web-applications to JPA. We are using
> GlassFish with TopLink, although there is nothing
> that forces us use
> TopLink, so we are ready to switch to something else
> if it can solve our
> problems.
>
> One thing I should note before asking the questions:
> we only read the data
> in our application and never modify, add or delete
> the data, so we don't
> care about persisting the data back. Moreover, we've
> only got the views of
> the actual tables and there is no way we can change
> the bad DB design, or
> even get better-structured views.
>
> Here are serveral questions/problems we've got:
>
> 1. Suppose we've got entity ChangeRequest (CR)
> which data is contained
> in table CHANGE_REQUESTS. For each CR there may be
> 0..n keywords which are
> associated to it. Keywords are simple strings, they
> reside in the table
> KEYWORDS and the columns of these table are
> (CHANGE_REQUEST_EXTRA_ID,
> KEYWORD, ...). CHANGE_REQUEST_EXTRA_ID is not a PK
> in CHANGE_REQUESTS table,
> but it is unique for each entity there. There are
> actually quite a bunch of
> other fields in KEYWORDS table (like DATE_CREATED,
> DATE_MODIFIED, etc.), but
> they are completely unnecessary. The only thing we
> are interested in is the
> collection of the keywords (Strings) associated to
> the CR. Is it possible to
> do without an extra entity for a keyword, so that I
> could have a
> "Collection<String> keywords;" in the CR class,
> instead of
> "Collection<Keyword> keywords;"? Is there any way I
> can get a Collection of
> basic types (like String) from the EntityManager
> query?
> 2. Is it possible to make the KEYWORDS table as a
> SecondaryTable for
> CRs (remember that we have one-to-many relation)?
> Would we be able to have a
> "Collection<String> keywords"-kind of field in our
> CR entity then? If so,
> would these keywords be fetched in a separate query
> from the query which
> gets the CR information, or would there be a single
> query with a JOIN and
> thus a lot of rows would be returned with only the
> KEYWORD column being
> different?
> 3. Suppose we've got the many-to one relation
> between CRs and CRs: for
> each CR there may exist a main CR, and one main CR
> may have many CRs
> associated with it. We need to do the following
> query (in terms of SQL):
> > SELECT cr2.cr_number FROM change_requests cr1
> > JOIN change_requests cr2
> > ON (cr1.mr_number != 0 AND cr1.mr_number =
> cr2.mr_number)
> > OR cr1.cr_number = cr2.cr_number
> > WHERE cr1.cr_number = ? AND cr2.release = ?
>
> cr_number is a PK, mr_number is a column with the
> id of the main CR if
> it exists, or 0 if it doesn't. First, I tried to
> express this query JPQL,
> but I failed to express the join-criteria. I would
> love to see how that can
> be done, if it is possible.
> If I use a NativeNamedQuery query like above, and
> try to get the
> result as ChangeRequest entity, I can't do that
> either: it seems that
> TopLink cannot work with the aliased column names
> and I get the following
> exception:
> Exception [TOPLINK-6044] (Oracle TopLink
> Essentials - 2.0 (Build
> b58g-fcs (09/07/2007))):
> oracle.toplink.essentials.exceptions.QueryException
> Exception Description: The primary key read from
> the row
> [DatabaseRecord(
> => 1234567)] during the execution of the query
> was detected to
> > be null. Primary keys must not contain null.
> > Query: ReadAllQuery(foo.bar.ChangeRequest)
>
>
> Is it possible to do at all? I tried to do the
> JOIN without aliasing
> the second table to cr2, but that gave me the
> Oracle DB error "column
> ambiguosly defined". Selecting cr2.* doesn't help
> too (in that case we get
> DatabaseRecord( => 1234567, => asdfasdf, ...)] in
> the exception message.
> Thanks,
> Ivan
> [att1.html]
Hi everyone,
For the mapping case of List <? extends someClass>, it is clear to see that this mapping is a combination of class association (One-to-Many) and inheritance.
I can handle this mapping, database schema can be generated, storing and retrieving objects also no any problem.
But I encounter the problem of over-writing the old list in database with the new list in client code even though I have used "DELETE_ORPHAN" extended annotation from Hibernate.
Please notice that, for the mapping case of List<someConcreteClass>, the "DELETE_ORPHAN" extended annotation can help to solve the problem.
But for the mapping of List<? extend someClass>, it does not help at all.
I always get the following error:
[b]org.hibernate.HibernateException: A collection with cascade="all-delete-orphan" was no longer referenced by the owning entity instance[/b]
Attached is the class diagram for the data model which describe that a Person has a list of BillingDetails which can be either BankAccount or CreditCard
Any reply, suggestion or help is very welcome.
Thanks much
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