I have the following problem, the whole system uses a relation, Eager, but for a specific query I do not want to bring all the relations in the database, because it would be very cumbersome, just for this query I can change the parameter to Lazy ?
I'm using EJB, JNDI, JPA and EclipseLink
Natively there is no way to leave data like Lazy, yet.
Below I suggest how to work around or deal with this problem.
Depending on the relationship, there is no problem in leaving the relationship as EAGER. Something like:
@OneToMany(fetchType = EAGER)
List<Email> emails; // sendo que aqui teria no max 3 emails
@OneToMany(fetchType = EAGER)
List<PerfilUsuario> perfil; // um usuário teria uns 2 perfis como Gerente e Usuario
Note that for collections that will have little data, it is okay to leave EAGER. Now the problem is if this becomes practice and all the attributes become EAGER, it will detonate with the server's memory.
It is best that your LAZY relationships, those ending in * Many, are always LAZY. To do this, it would be enough to leave your relationships as:
@OneToMany
List<Email> emails;
@OneToMany
List<PerfilUsuario> perfil;
And the query being performed through JPQLs like: select p from Person p join fetch p.Emails and
You search only what is required to be displayed on the screen. Why this solution is a good practice:
Well, it has more advantages but only with these I believe that already it is possible to show that to look for only the necessary is already the best solution.
To query with JPQL by selecting only the required entities.
With JPQL you can force joins to LAZY relationships or select only a few attributes.
In the latter case, use a native query.