Using Metamodel Classes

Metamodel classes that correspond to entity classes are of the following type:

javax.persistence.metamodel.EntityType<T>

Metamodel classes 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 by using the persistence provider’s annotation processor or may obtain the metamodel class by either 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.

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();

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

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