JPA find() & getReference()

in javax.persistence.EntityManager

* find(): always call select from DB

Use for select one entity from DB.

Example:

Game game = entityManager.find(Game.class, 1L);

* getReference(): Objecre returned is an entity that only has primary key field initialized. The other field remain unset unless we request them.

Use for update, delete.

Example :

Game game = entityManager.getReference(Game.class, 1L);

// update it-self
game1.setName("Game Updated 1");
entityManager.persist(game1);

//update parent of it
Player player1 = entityManager.find(Player.class, 1L);
player1.setGame(game);
entityManager.persist(player1);

// delete it-self 

entityManager.remove(game)

Reference:
Post: https://www.baeldung.com/jpa-entity-manager-get-reference
Test: https://github.com/eugenp/tutorials/blob/master/persistence-modules/hibernate-jpa/src/test/java/com/baeldung/hibernate/entitymanager/getreference/GetReferenceMySQLManualTest.java