3.3. Loading an object

download PDF
Load an entity instance by its identifier value with the entity manager's find() method:
cat = em.find(Cat.class, catId);

// You may need to wrap the primitive identifiers
long catId = 1234;
em.find( Cat.class, new Long(catId) );
In some cases, you don't really want to load the object state, but just having a reference to it (ie a proxy). You can get this reference using the getReference() method. This is especially useful to link a child to its parent without having to load the parent.
child = new Child();
Parent parent = em.getReference(Parent.class, parentId); //no query to the DB
You can reload an entity instance and its collections at any time using the em.refresh() operation. This is useful when database triggers are used to initialize some of the properties of the entity. Note that only the entity instance and its collections are refreshed unless you specify REFRESH as a cascade style of any associations:
em.flush(); // force the SQL insert and triggers to run
em.refresh(cat); //re-read the state (after the trigger executes)
Red Hat logoGithubRedditYoutubeTwitter


Try, buy, & sell


About Red Hat Documentation

We help Red Hat users innovate and achieve their goals with our products and services with content they can trust.

Making open source more inclusive

Red Hat is committed to replacing problematic language in our code, documentation, and web properties. For more details, see the Red Hat Blog.

About Red Hat

We deliver hardened solutions that make it easier for enterprises to work across platforms and environments, from the core datacenter to the network edge.

© 2024 Red Hat, Inc.