T getReference(
  Class<T> entityClass, 
  Object primaryKey
)

Obtain a reference to an instance of the given entity class with the given primary key, whose state may be lazily fetched.

If the requested instance does not exist in the database, the EntityNotFoundException is thrown when the instance state is first accessed. (The persistence provider runtime is permitted but not required to throw the EntityNotFoundException when getReference() is called.)

This operation allows the application to create an association to an entity without loading its state from the database.

The application should not expect the instance state to be available upon detachment, unless it was accessed by the application while the entity manager was open.