Mapping a list of Java 8 month enum in Hibernate

Question

is it possible to map a list of java.time.Month to a seperate Table like so:

|MyEntity             |    |MyEntity_Month    |    |Month          |
|---------------------|    |------------------|    |---------------|
|id : long            |    |myEntity_Id : long|    |id : long      |
|                     |----|month_Id : long   |----|               |
|---------------------|    |------------------|    |---------------|

I have tried it like this but it that only creates a table MyEntity_Month with a myEntity_Id and values:

@ElementCollection(targetClass = Month.class, fetch = FetchType.EAGER)
@Enumerated(EnumType.STRING)
@CollectionTable(name = "MyEntity_Months"
        , joinColumns = @JoinColumn(name = "myEntity_id"))
private List<Month> months;

The problem with that solution is that the values are repeated for each MyEntity instead of associated. Database view of the above annotation configuration:

|MyEntity             |    |MyEntity_Month         | 
|---------------------|    |-----------------------|
|id : long            |    |myEntity_id | MONTH    |
|...                  |----|-----------------------|
|---------------------|    |1           | NOVEMBER |
                           |1           | DECEMBER |
                           |2           | JANUARY  |
                           |2           | DECEMBER |
                           |-----------------------|

Is it possible to map via assocation table so that I need only 12 Month Strings in the database? I'm using Hibernate 4.3 / JPA 2.1 btw

Answer 1

The type java.time.Month does not have @Entity annotations, so this is not recognized as an entity by hibernate. You can achieve your desired table mapping if you introduce something like a MonthWrapper:

@Entity
public class MyEntity {

    @Id
    private Long id;

    @OneToMany(fetch = FetchType.EAGER)
    private List<MonthWrapper> months;
}


@Entity
public class MonthWrapper {

    @Id
    private Long id;

    @Enumerated(EnumType.STRING)
    private Month month;
}

Then if you run this through hibernate with a create-drop hbm2ddl.auto property, then you get the following tables:

Hibernate: create table MonthWrapper (id bigint not null, month varchar(255), primary key (id))

Hibernate: create table MyEntity (id bigint not null, primary key (id))

Hibernate: create table MyEntity_MonthWrapper (MyEntity_id bigint not null, months_id bigint not null)