Pavel Buzek wrote:
> try this:
>
> // Merge the detached entity back in
> -- em.merge(subscription);
> ++ subscription = em.merge(subscription);
>
> -pavel
D'oh ... the examples even show that kind of code ... it works now.
Thanks Gordon and Pavel!
Craig
>
> Craig McClanahan wrote:
>
>> I'm experimenting with the new JPA APIs by writing some simple
>> CRUD-based examples. Add, update, and display all work great ... but
>> I'm running into an exception (documented below) when trying to
>> remove a detail row. I am using Glassfish Build 48, and building the
>> test code with NB 5.5 beta.
>>
>> I've got two entity classes that, among other things, have a
>> bidirectional one-to-many relationship with each other:
>>
>> @Entity
>> public class User implements Serializable {
>> ....
>> @OneToMany(mappedBy="user")
>> private List<Subscription> subscriptions;
>> ...
>> public List<Subscription> getSubscriptions() { return
>> this.subscriptions; }
>> public void setSubscriptions(List<Subscription> subscriptions) {
>> this.subscriptions = subscriptions;
>> }
>> ...
>> }
>>
>>
>> @Entity
>> public class Subscription implements Serializable {
>> ...
>> @ManyToOne
>> private User user;
>> ...
>> public User getUser() { return this.user; }
>> public void setUser(User user) { this.user = user; }
>> ...
>> }
>>
>> Note that the above classes correctly implement hashCode() and
>> equals() as well ... without that the comparisons performed would be
>> failing.
>>
>> According to the JPA specification, it is the application's
>> responsibility to maintain the properties that implement the
>> relationship, so I've added a convenience method to the User class
>> like this:
>>
>> public void removeSubscription(Subscription subscription) {
>> if ((subscriptoin == null) || (subscriptions == null)) {
>> return;
>> }
>> if (subscriptions.contains(subscription)) {
>> subscriptions.remove(subscription);
>> subscription.setUser(null);
>> }
>> }
>>
>> Now, my business logic looks like this:
>>
>> @PersistenceContext
>> EntityManager em; // Injected for me
>>
>> @Resource
>> UserTransaction utx; // Injected for me
>>
>> Subscription subscription = ...; // A detached copy of a
>> Subscription entity
>> // Start a transaction
>> utx.begin();
>> // Merge the detached entity back in
>> em.merge(subscription);
>> // Attempt to remove the subscription
>> subscription.getUser().removeSubscription(subscription);
>> // Remove the subscription from the database too
>> em.remove(subscription);
>> // Complete the transaction
>> utx.commit();
>>
>> However, I get an exception from TopLink Essentials that looks like
>> this:
>>
>> java.lang.NullPointerException
>> at
>> oracle.toplink.essentials.internal.indirection.UnitOfWorkValueHolder.instantiate(UnitOfWorkValueHolder.java:217)
>>
>> at
>> oracle.toplink.essentials.internal.indirection.DatabaseValueHolder.getValue(DatabaseValueHolder.java:82)
>>
>> at
>> oracle.toplink.essentials.indirection.IndirectList.buildDelegate(IndirectList.java:193)
>>
>> at
>> oracle.toplink.essentials.indirection.IndirectList.getDelegate(IndirectList.java:315)
>>
>> at
>> oracle.toplink.essentials.indirection.IndirectList.contains(IndirectList.java:249)
>>
>> at myjpaexample.User.removeSubscription(User.java:99)
>>
>>
>> where line 99 in User is the line inside removeSubscription() that
>> calls "subscriptions.contains()". Various attempts to remove the
>> subscription from the list by other means all seem to end up with an
>> NPE at the same place.
>>
>> Any ideas?
>>
>> Craig McClanahan
>>
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