Best practice of mapping collection of enum

[manuel aldana]

Hi,

I am having a list assoziation to enums:

class User{
List<RoleAsEnum> roles;
}


As such with O/R this would get mapped with a join to two tables because of the 1:n relation. For enum reasons one could also consider to use a third join-table, so enum-entries aren't repeated inside the enum table all the time.

Never the less I would like to avoid joins (enums are stupid types and I don't consider them as entities but rather as table-column).

I thought about writing a custom converter, so the enum is serialized into a comma separated string, but I think such an encoding as kind of bad practice. Is there maybe a JPA + hibernate homegrown solution for mapping the 1:n(asEnum) relation?

thanks.

[Emanuel Kadziela]

I always wrap my enums in persistable enum entities and map those, providing an easy way to get the actual enum out of the enum entity wrapper. For example:

    
public enum SomeEnum
{
SOME,ENUM
}
@Entity
public class SomeEnumEntity
{
@Id @GeneratedValue
private Long id;

@Enumerated
private SomeEnum someEnum

@ManyToOne
private User user;
}

@Entity
public class User
{
@Id @GeneratedValue
private Long id;

@OneToMany(mappedBy = "user")
private Collection<SomeEnumEntity> someEnumEntities;
}

The above gives you a simple 2 table bidirectional one-to-many / many-to-one relationship between an enum and an entity which needs a collection of those enums. All you have to do is fill out the usual rest of the bean stuff as well as a way to manage the wrapper correctly (i.e. to get and set the enum itself inside it).