Max Ross, I took time to review and enter discussion relating to your
snippet. In that thread above I raised questions, but never heard
back...please have a look.
On Nov 2, 12:55 pm, "Max Ross (Google)" <maxr+appeng...@google.com>
wrote:
> Looking in the debugger is not a good indication of what is and is not set
> because jdo-enhanced classes perform lazy loading when the fields are
> accessed. If you call a getter method and System.out.println() the result
> is it still null? Feel free to send me your model objects and your
> persistence code with some println()s showing me the problem and I'll have a
> look.
>
> Max
>
>
>
> On Tue, Oct 27, 2009 at 5:28 PM, stanlick <stanl...@gmail.com> wrote:
>
> > Hey Max --
>
> > At what point are you validating this? I am breaking after the commit
> > and also after a subsequent query.execute(). Dude, it is about to
> > make me jump off a bridge.
>
> > P.S. I'm not a good swimmer, so please throw me a clue.
>
> > Scott
>
> > On Oct 27, 12:25 pm, "Max Ross (Google)"
> > <maxr+appeng...@google.com<maxr%2bappeng...@google.com>
>
> > wrote:
> > > At what point are you checking to see if the parent property of the child
> > is
> > > populated? I see that the newly created Chapter's Book property is
> > > populated when addChapterToBook() completes.
>
> > > Max
>
> > > On Tue, Oct 27, 2009 at 8:31 AM, stanlick <stanl...@gmail.com> wrote:
>
> > > > This code saves the child for me, however, the parent property of the
> > > > child (in your case "book") is null in the child. I have tried
> > > > deliberately setting this child "parent" property myself to the parent
> > > > prior to commit, but nothing seems to work.
>
> > > > On Sep 28, 6:45 pm, Max Ross
> > > > <maxr+appeng...@google.com<maxr%2bappeng...@google.com>
> > <maxr%2bappeng...@google.com <maxr%252bappeng...@google.com>>>
> > > > wrote:
> > > > > Hello again and welcome to Episode 3 of JDO/JPA Snippets That Work.
> > > > Today's
> > > > > episode is called......
>
> > > > > Updating A Bidrectional Owned One-To-Many With A New Child
>
> > > > > All the way back in episode one we demonstrated how to create both a
> > > > parent
> > > > > and a child of a bidirectional, owned, one-to-many relationship
> > > > > at the same time. This week we're going to see how to add a child to
> > an
> > > > > existing parent. We'll use the same model objects we used in episode
> > > > one:
>
> > > > > JPA:
> > > > > @Entity
> > > > > public class Book {
> > > > > @Id
> > > > > @GeneratedValue(strategy=GenerationType.IDENTITY)
> > > > > private Key id;
>
> > > > > private String title;
>
> > > > > @OneToMany(mappedBy = "book", cascade = CascadeType.ALL)
> > > > > private List<Chapter> chapters = new ArrayList<Chapter>();
>
> > > > > // getters and setters
>
> > > > > }
>
> > > > > @Entity
> > > > > public class Chapter {
> > > > > @Id
> > > > > @GeneratedValue(strategy=GenerationType.IDENTITY)
> > > > > private Key id;
>
> > > > > private String title;
> > > > > private int numPages;
>
> > > > > @ManyToOne(fetch = FetchType.LAZY)
> > > > > private Book book;
>
> > > > > // getters and setters
>
> > > > > }
>
> > > > > Now let's assume we've already created a book with a few chapters in
> > the
> > > > > datastore and we want to add a brand new chapter to a Book with a
> > given
> > > > id
> > > > > (we'll assume someone else is creating and closing an EntityManager
> > named
> > > > > 'em' for us):
>
> > > > > public void addChapterToBook(EntityManager em, Key bookKey, Chapter
> > > > chapter)
> > > > > {
> > > > > em.getTransaction().begin();
> > > > > try {
> > > > > Book b = em.find(Book.class, bookKey);
> > > > > if (b == null) {
> > > > > throw new RuntimeException("Book " + bookKey + " not
> > > > found!");
> > > > > }
> > > > > b.getChapters().add(chapter);
> > > > > em.getTransaction().commit();
> > > > > } finally {
> > > > > if (em.getTransaction().isActive()) {
> > > > > em.getTransaction().rollback();
> > > > > }
> > > > > }
>
> > > > > }
>
> > > > > JDO:
>
> > > > > @PersistenceCapable(identityType = IdentityType.APPLICATION,
> > detachable =
> > > > > "true")
> > > > > public class Book {
>
> > > > > @PrimaryKey
> > > > > @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> > > > > private Key id;
>
> > > > > private String title;
>
> > > > > @Persistent(mappedBy = "book")
> > > > > @Element(dependent = "true")
> > > > > @Order(extensions = @Extension(vendorName="datanucleus", key=
> > > > > "list-ordering", value="id asc"))
> > > > > private List<Chapter> chapters = new ArrayList<Chapter>();
>
> > > > > // getters and setters
>
> > > > > }
>
> > > > > @PersistenceCapable(identityType = IdentityType.APPLICATION,
> > detachable =
> > > > > "true")
> > > > > public class Chapter {
> > > > > @PrimaryKey
> > > > > @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY)
> > > > > private Key id;
>
> > > > > private String title;
> > > > > private int numPages;
>
> > > > > @Persistent
> > > > > private Book book;
>
> > > > > // getters and setters
>
> > > > > }
>
> > > > > Now let's assume we've already created a book with a few chapters in
> > the
> > > > > datastore and we want to add a brand new chapter to a Book with a
> > given
> > > > id
> > > > > (we'll assume someone else is creating and closing a
> > PersistenceManager
> > > > > named 'pm' for us):
>
> > > > > public void addChapterToBook(PersistenceManager pm, Key bookKey,
> > Chapter
> > > > > chapter) {
> > > > > pm.currentTransaction().begin();
> > > > > try {
> > > > > // throws a runtime exception if book is not found
> > > > > Book b = pm.getObjectById(Book.class, bookKey);
> > > > > b.getChapters().add(chapter);
> > > > > pm.currentTransaction().commit();
> > > > > } finally {
> > > > > if (pm.currentTransaction().isActive()) {
> > > > > pm.currentTransaction().rollback();
> > > > > }
> > > > > }}
>
> > > > > --------------------------------
>
> > > > > The interesting thing about both of these examples is that we're not
> > > > making
> > > > > any explicit calls to save the new Chapter. We look up the Book
> > > > identified
> > > > > by the Key that was passed into the function and then we manipulate
> > the
> > > > > persistent state of the object by manipulating the POJO that was
> > returned
> > > > by
> > > > > em.fetch/pm.getObjectById. JPA and JDO both have mechanisms that
> > allow
> > > > them
> > > > > to monitor the objects that you've looked up for changes. Ever
> > wonder
> > > > what
> > > > > exactly the enhancer is doing to your classes? It's adding hooks so
> > that
> > > > > the persistence framework gets notified when things change (among
> > other
> > > > > things). This allows JPA and JDO to automatically flush your changes
> > to
> > > > the
> > > > > datastore when you commit your transaction. If you wanted to modify
> > the
> > > > > title of the Book or the number of pages in an existing Chapter the
> > > > approach
> > > > > would be exactly the same: Start a transaction, look up the Book,
> > make
> > > > your
> > > > > changes, commit your transaction. Whether you're using JPA or JDO
> > your
> > > > > changes will be persisted for you without any explicit calls to
> > change
> > > > the
> > > > > persistent state. This is a prime example of how JPA and JDO
> > facilitate
> > > > > "transparent persistence."- Hide quoted text -
>
> - Show quoted text -
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