Using Metamodel Classes

Metamodel classes that correspond to entity classes are of type javax.persistence.metamodel.EntityType<T>, and are typically generated by annotation processors either at development time or at runtime. Developers of applications that use Criteria queries may generate static metamodel classes using the persistence provider's annotation processor, or may obtain the metamodel class either by calling the getModel method on the query root object or first obtaining an instance of the Metamodel interface and then passing the entity type to the instance's entity method.

Example 22–3 Obtaining a Metamodel Class Dynamically Using the Root<T>.getModel Method

The following code snippet shows how to obtain the Pet entity's metamodel class by calling Root<T>.getModel.

EntityManager em = ...;
CriteriaBuilder cb = em.getCriteriaBuilder();
CriteriaQuery cq = cb.createQuery(Pet.class);
Root<Pet> pet = cq.from(Pet.class);
EntityType<Pet> Pet_ = pet.getModel();

Example 22–4 Obtaining a Metamodel Class Dynamically Using the Metamodel.getMetamodel Method

The following code snippet shows how to obtain the Pet entity's metamodel class by first obtaining a metamodel instance using EntityManager.getMetamodel, and then calling entity on the metamodel instance.

EntityManager em = ...;
Metamodel m = em.getMetamodel();
EntityType<Pet> Pet_ = m.entity(Pet.class);