persistence

I'm try to use the Sun Java PetStore Demo. In the CatalogFacade class there is the following annotation: @PersistenceUnit(unitName="myPetStorePU") private EntityManagerFactory emf; In all the methods of the CatalogFacade Sun has: EntityManager em = emf.createEntityManager(); But I am getting a null pointer exception for emf when trying to createEntityManager. But... if I add the following line above that line as such EntityManagerFactory emf = javax.persistence.Persistence.createEntityManagerFactory("myPetStorePU"); EntityManager em = emf.createEntityManager(); then emf gets successfully

What exactly is the difference in the following two declarations B is the owning side @Entity class A { @Id int id; @OneToOne B b; } @Entity class B { @Id int id; @OneToOne(mappedBy="b") A a; } A is the owning side @Entity class A { @Id int id; @OneToOne(mappedBy="a") B b; } @Entity class B { @Id int id; @OneToOne A a; } Thinking of this in "normal SQL" i think it is the same as having two tables each having the other table's foreign key. What i don't understand though is what is the effect of specifying which entity is the owning side i.e using the 'mappedBy' property. What does this actually

I'm developing an app which will save data to the local file system. The data that will be saved will be mostly NSString and NSDate. The data will not be saved that often, perhaps new data will be entered 10 times at a typical usage. The data should also of course be retrievable (CRUD) How should I save this data? First of all is it necessary to model these objects? If not should I use property lists? Or SQLLite3? Else should I archive the class models? Use SQLLite3? EDIT: I accidentally left out some vital information about the app. Actually my app will be having 2 data models which have an

The PHP script is as follows: <?php // continue.php ini_set('session.gc_maxlifetime', 5); session_start(); echo ini_get('session.gc_maxlifetime'); // wait for 7 seconds usleep(7000000); if (isset($_SESSION['username'])) { $username = $_SESSION['username']; $password = $_SESSION['password']; $forename = $_SESSION['forename']; $surname = $_SESSION['surname']; echo "Welcome back $forename.<br /> Your full name is $forename $surname.<br /> Your username is '$username' and your password is '$password'."; } else echo "Please <a href=authenticate2.php>click here</a> to log in."; ?> Based on the

Most projects have some sort of data that are essentially static between releases and well-suited for use as an enum, like statuses, transaction types, error codes, etc. For example's sake, I'll just use a common status enum: public enum Status { ACTIVE(10, "Active"); EXPIRED(11, "Expired"); /* other statuses... */ /* constructors, getters, etc. */ } I'd like to know what others do in terms of persistence regarding data like these. I see a few options, each of which have some obvious advantages and disadvantages: Persist the possible statuses in a status table and keep all of the possible

My application users asked if it were possible for pages that contain a jqGrid to remember the filter, sort order and current page of the grid (because when they click a grid item to carry out a task and then go back to it they'd like it to be "as they left it") Cookies seem to be the way forward, but how to get the page to load these and set them in the grid before it makes its first data request is a little beyond me at this stage. Does anyone have any experience with this kind of thing with jqGrid? Thanks! PROBLEM SOLVED I eventually ended up using cookies in javascript to store the sort