JPA脱离结果

Question

My code:

String sql = SELECT * FROM users;

List<Users> users = entityManager.createNativeQuery(sql, Users.class); 

for(Users i : users) 
   entityManager.detach(i); 

How to replace this boilerplate loop:

for(Users i : users) 
   entityManager.detach(i); 

?

It is a simple example but imagine that every object has the 20 of neested objects then it would look like this:

for(Users i : users) 
{
       entityManager.detach(i); 
        for(Users y : i.getNeested()) 
        {
             entityManager.detach(y);
             for(Users y : i.getNames()) 
              ....
        }
}

Answer 1

Perform the query in a transaction by itself. Once the transaction ends, the results won't be attached to the persistence context any more.

Simple example, no separate detaching necessary. Make sure to use a REQUIRES_NEW if you have an on-going transaction, otherwise they won't be detached.

@Transactional(propagation=Propagation.REQUIRES_NEW)
@Override
public List<User> findUsers() {
    return em.createNativeQuery("SELECT * FROM users", User.class).getResultList();
}