Well - as mentioned in previous blog entry I've written a tiny framework to make it easier to store (kinda) POJO's in Google App Engine for Java. This will try to explain what I've got running so far:
@Test
public void testCreateWishlistAndAddRecipient() {
UnitOfWork uow = new GAEUnitOfWork();
All work with entities are done in the scope of a unit of work (UnitOfWork) which is transactional and only for a single entity-group at a time, since GAE/J can only handle transactions within a single entity-group, its very important not to hide this fact from users.
Date created = new Date();
Wishlist wishlist = uow.newEntity(Wishlist.class);
wishlist.title().set("Wishlist for christmas 2009");
wishlist.comment().set("No soft presents");
wishlist.created().set(created);
To create a new entity (in this case entity-group as there are no parents) you use "newEntity" which will return an instance of the class given as second argument.
uow.complete();
"uow.complete" will make all changes persistent using GAE low-level API.
uow = new GAEUnitOfWork();
wishlist = uow.get(wishlist.getEntityReference());
assertEquals("Wishlist for christmas 2009", wishlist.title().get());
assertEquals("No soft presents", wishlist.comment().get());
assertEquals(created, wishlist.created().get());
Well - check to make sure all is persistent as expected...
Recipient recipient1 = uow.newEntity(wishlist, Recipient.class);
recipient1.name().set("Test Person #1");
recipient1.email().set(new Email("testperson1@email.com"));
In this example a Wishlist holds a ManyAssociation
which is a collection of Recipient objects. The above creates a new Recipient, which will be stored as a child GAE Entity of the Wishlist Entity (not a Key reference) and therefore it's parent (wishlist) if given as argument in "newEntity(wishlist, Recipient.class)
Recipient recipient2 = uow.newEntity(wishlist, Recipient.class);
recipient2.name().set("Test Person #2");
recipient2.email().set(new Email("testperson2@email.com"));
wishlist.recipients().add(recipient1);
wishlist.recipients().add(recipient2);
uow.complete();
Finally the newly created 2 Recipient objects are added to the "wishlist.recipients()" ManyAssociation (collection) and UnitOfWork is complete (all objects persistet)
uow = new GAEUnitOfWork();
wishlist = uow.get(wishlist.getEntityReference());
ManyAssociation recipients = wishlist.recipients();
assertEquals(2, recipients.getCount());
assertEquals("Test Person #1", recipients.get(0).name().get());
assertEquals("testperson1@email.com", recipients.get(0).email().get().getEmail());
assertEquals("Test Person #2", recipients.get(1).name().get());
assertEquals("testperson2@email.com", recipients.get(1).email().get().getEmail());
}
... and again tests to check all were persistet as expected.
Next up - a look under the hood where child objects are all lazy loaded.
