That is very nice.
This isn't meant to rain on Twig's parade, but if you're going the JDO route
you can also use generics to simplify things via a generic dao;
abstract class AbstractJdoDao<E> extends JdoDaoSupport {
protected final transient Logger log = LoggerFactory.getLogger(getClass());
protected final Class<E> entityClass;
AbstractJdoDao(final Class<E> _entityClass, final PersistenceManagerFactory
pmf) {
this.entityClass = _entityClass;
setPersistenceManagerFactory(pmf);
}
public E findById(final String id) {
final E result =
getPersistenceManager().getObjectById(this.entityClass, id);
return (getPersistenceManager().detachCopy(result));
}
Then my FacilityDao starts with
@Repository
public class FacilityDao extends AbstractJdoDao<Facility> {
/**
* @param pmf
*/
@Autowired
public FacilityDao(final PersistenceManagerFactory pmf) {
super(Facility.class, pmf);
}
Notice how it passes the class it's working with, which is stored in the
abstract dao as entityClass.
Still not as easy as Twig though!
John Patterson wrote:
> Just to show how easy this sort of query and mapping is in Twig.
> Notice the lack of Keys - the Book id is optional.
>
> public class Book {
> private long id;
> private String title;
>
> @Entity(Child)
> private List<Chapter> chapters = new ArrayList<Chapter>();
> }
>
> The @Entity(Child) annotation applies to all the elements of the
> collection
>
> public class Chapter {
>
> @Key
> private String title;
> private int numPages;
>
> @Entity(Parent)
> private Book book;
> }
>
> The Chapter title has been configured to be the key name so it is
> automatically encoded in the key.
>
> Getting the book is as easy as:
>
> session.find(Chapter.class, "War and Peace").getBook()
>
> Notice that because Twig was written from scratch using generics the
> result of find() is known to be a Chapter so we can then just call
> getBook() on the result.
>
> http://code.google.com/p/twig-persist/
>
> On 3 Nov 2009, at 00:03, Solvek wrote:
>
>> Now. How to retrieve a book and its chapters having only Chapter's
>> title (imagine all titles in whole systems are unique)
>>
>> On Sep 15, 1:07 am, Max Ross <[email protected]> wrote:
>>> Hello hello and welcome to the very first installment of JDO/JPA
>>> Snippets
>>> That Work!
>>>
>>> Creating A Bidrectional Owned One-To-Many
>>>
>>> Suppose you're building a book catalog application and you want to
>>> model
>>> books and chapters. Books contain chapters. A chapter cannot
>>> exist without
>>> a book, so if you delete a book you want its chapters automatically
>>> deleted
>>> along with it. You also want to each chapter to have a reference
>>> to the
>>> book that owns it. Sounds like a bidrectional, owned, one-to-many
>>> relationship is just the thing. First we'll set up our model
>>> objects and
>>> then we'll add some code to create a Book with 2 Chapters.
>>>
>>> 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 create a book with two chapters (we'll assume someone
>>> else is
>>> creating and closing an EntityManager named 'em' for us):
>>>
>>> Book b = new Book();
>>> b.setTitle("JPA 4eva");
>>> Chapter c1 = new Chapter();
>>> c1.setTitle("Intro");
>>> c1.setNumPages(10);
>>> b.getChapters().add(c1);
>>> Chapter c2 = new Chapter();
>>> c2.setTitle("Configuration");
>>> c2.setNumPages(9);
>>> b.getChapters().add(c2);
>>>
>>> em.getTransaction().begin();
>>> try {
>>> em.persist(b);
>>> 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")
>>> 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 create a book with two chapters (we'll assume someone
>>> else is
>>> creating and closing a PersistenceManager named 'pm' for us):
>>>
>>> Book b = new Book();
>>> b.setTitle("JDO 4eva");
>>> Chapter c1 = new Chapter();
>>> c1.setTitle("Intro");
>>> c1.setNumPages(10);
>>> b.getChapters().add(c1);
>>> Chapter c2 = new Chapter();
>>> c2.setTitle("Configuration");
>>> c2.setNumPages(9);
>>> b.getChapters().add(c2);
>>>
>>> pm.currentTransaction().begin();
>>> try {
>>> pm.makePersistent(b);
>>> pm.currentTransaction().commit();} finally {
>>>
>>> if (pm.currentTransaction().isActive()) {
>>> pm.currentTransaction().rollback();
>>> }
>>>
>>> }
>
>
> >
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