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 Post subject: Replacing @Formula with a proper @ElementCollection mapping
PostPosted: Tue Aug 02, 2016 9:07 am 
Newbie

Joined: Tue Aug 02, 2016 7:51 am
Posts: 6
I've stumbled upon a situation i cannot resolve using Hibernate documentation - i cannot alter an @ElementCollection from within the corresponding entity or even the DAO/Service.
My setup has a hibernate entity, separated into two classes:

Code:
@Entity
@Table(name = "PERSON")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="type",discriminatorType=DiscriminatorType.STRING)
@DiscriminatorValue(value="person")
public class Person implements PersonInterface{
    ...
    @ElementCollection
    @Formula("(SELECT groupId FROM PERSON_GROUPS WHERE id = id)")
    protected List<Integer> groups = new ArrayList<>();
    ...
    @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.MERGE)
    @JoinTable(name = "user_roles", joinColumns = {
        @JoinColumn(name = "USER_ID", nullable = false, updatable = false)},
        inverseJoinColumns = { @JoinColumn(name = "ROLE_ID", nullable = false, updatable = false)})
    protected List<Role> roles = new ArrayList<>();

Code:
@Entity
@DiscriminatorValue("mutableperson")
public class MutablePerson extends Person implements MutablePersonInterface{
    ...
    public void excludeFromRole(Integer roleId){
        roles.remove(roleId);
    }

    public void excludeFromGroup(Integer groupId){
        groups.remove(groupId);
    }
}

The thing is, while excludeFromRole works, excludeFromGroup throws an exception "failed to lazily initialize a collection of role". I thought that had something to do with no open sessions, etc., but even when i explicitly call excludeFromGroup in DAO with an entityManager, it still returns the same exception.
I tried detaching the entity with EntityManager or closing the session in which it was fetched from the DB, but it didn't help.
This page https://docs.jboss.org/hibernate/orm/5. ... rmula.html says, that Formula represents a read-only state. Does this mean what i'm trying to do is effectively impossible and i have to look at @ColumnTransformer (which i can't get to work properly so far)?


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 Post subject: Re: Altering @Formula annotated @ElementCollection
PostPosted: Tue Aug 02, 2016 9:38 am 
Hibernate Team
Hibernate Team

Joined: Thu Sep 11, 2014 2:50 am
Posts: 1630
Location: Romania
Just as you concluded, @Formula gives you a read-only mapping, so you cannot benefit from the very convenient dirty checking mechanism.

What you need to do is to replace @Formula with a proper @ElementCollection mapping. For this, the groups mapping becomes:

Code:
@ElementCollection
@CollectionTable(
    name="PERSON_GROUPS",
    joinColumns=@JoinColumn(name="id")
)
@Column(name="groupId")
protected List<Integer> groups = new ArrayList<>();


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 Post subject: Re: Replacing @Formula with a proper @ElementCollection mapping
PostPosted: Tue Aug 02, 2016 10:50 am 
Newbie

Joined: Tue Aug 02, 2016 7:51 am
Posts: 6
Ok, that seems to work in @Transactional context, thank you.

I don't understand, though, what's the difference between calling remove on those 2 fields:
Code:
    @ElementCollection
    @CollectionTable(
            name="PERSON_GROUPS",
            joinColumns=@JoinColumn(name="PERSON_USER_ID")
    )
    @Column(name="GROUP_ID")
    protected List<Integer> groups = new ArrayList<>();

   @ManyToMany(fetch = FetchType.LAZY, cascade = CascadeType.MERGE)
   @JoinTable(name = "user_roles", joinColumns = {
         @JoinColumn(name = "USER_ID", nullable = false, updatable = false)},
         inverseJoinColumns = { @JoinColumn(name = "ROLE_ID", nullable = false, updatable = false)})
   protected List<Role> roles = new ArrayList<>();

Even though both are lazily accessed, Roles can be changed without any opened session, and Groups - not so much.
Is there a way to make something like this work, without the need to use DAO as a proxy?
Code:
MutablePerson personFromDb = (MutablePerson) personService.getMutablePersonById(0);
personFromDb.excludeFromGroup(0);


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 Post subject: Re: Replacing @Formula with a proper @ElementCollection mapping
PostPosted: Tue Aug 02, 2016 2:28 pm 
Hibernate Team
Hibernate Team

Joined: Thu Sep 11, 2014 2:50 am
Posts: 1630
Location: Romania
I think you're making a wrong observation. Typically, if you try to modify an entity outside of a Transaction, you get an exception.


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 Post subject: Re: Replacing @Formula with a proper @ElementCollection mapping
PostPosted: Wed Aug 03, 2016 4:40 am 
Newbie

Joined: Tue Aug 02, 2016 7:51 am
Posts: 6
Indeed, with all the modifications i've made to the DAO during my "investigations", i forgot that in getEntityById() i was initializing Roles with Hibernate.initialize(), which was the cause of difference in behaviour.


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