How can you replicate Hibernate's saveOrUpdate in JPA?

Question

In JPA, is there any way you can replicate Hibernate\'s saveOrUpdate behavior,

saveOrUpdate

public void saveOrUpdate(Object object)
                  throws         


        

Answer 1

Try using the EntityManager.merge method - this is very similar.

There is an excellent description of the differences in Xebia's blogpost: "JPA Implementation Patterns: Saving (Detached) Entities."

Answer 2

The problem with the method outlined in the article that Pablojim linked to, is that it doesn't handle auto generated primary keys very well.

Consider the creation of a new ORM entity object, you can give this the same data as an existing row in the database table, but unless I am mistaken, the entity manager does not recognize them as the same row until they have the same primary key, which in a entity that uses auto generated keys, you can't get until you go up to the database.

Here is my current work around for that situation;

/**
 * Save an object into the database if it does not exist, else return
 * object that exists in the database.
 *
 * @param query query to find object in the database, should only return
 * one object.
 * @param entity Object to save or update.
 * @return Object in the database, whither it was prior or not.
 */
private Object saveOrUpdate(Query query, Object entity) {
    final int NO_RESULT = 0;
    final int RESULT = 1;

    //should return a list of ONE result, 
    // since the query should be finding unique objects
    List results = query.getResultList();
    switch (results.size()) {
        case NO_RESULT:
            em.persist(entity);
            return entity;
        case RESULT:
            return results.get(0);
        default:
            throw new NonUniqueResultException("Unexpected query results, " +
                    results.size());
    }
}