Mapping issue with multi-field primary keys using hibernate/JPA annotations

Question

Hi all,

I'm stuck with a database which is using multi-field primary keys. I have a situation where I have a master and details table, where the details table's primary key contains fields which are also the foreign key's the the master table. Like this:

Master primary key fields:
    master_pk_1

Details primary key fields:
    master_pk_1
    details_pk_2
    details_pk_3

In the Master class we define the hibernate/JPA annotations like this:

@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "idGenerator")
@Column(name = "master_pk_1")
private long masterPk1;

@OneToMany(cascade=CascadeType.ALL)
@JoinColumn(name = "master_pk_1", referencedColumnName = "master_pk_1")
private List<Details> details = new ArrayList<Details>();

And in the details class I have defined the id and back reference like this:

@EmbeddedId
@AttributeOverrides( { 
        @AttributeOverride( name = "masterPk1", column = @Column(name = "master_pk_1")),
        @AttributeOverride(name = "detailsPk2", column = @Column(name = "details_pk_2")),
        @AttributeOverride(name = "detailsPk2", column = @Column(name = "details_pk_2")) })
private DetailsPrimaryKey detailsPrimaryKey = new DetailsPrimaryKey();

@ManyToOne
@JoinColumn(name = "master_pk_1", referencedColumnName = "master_pk_1", insertable=false)
private Master master;

The goal of all of this was that I could create a new master, add some details to it, and when saved, JPA/Hibernate would generate the new id for master in the masterPk1 field, and automatically pass it down to the details records, storing it in the matching masterPk1 field in the DetailsPrimaryKey class. At least that's what the documentation I've been looking at implies.

What actually happens is that hibernate appears to corectly create and update the records in the database, but not pass the key to the details classes in memory. Instead I have to manually set it myself.

I also found that without the insertable=true added to the back reference to master, that hibernate would create sql that had the master_pk_1 field listed twice in the insert statement, resulting in the database throwing an exception.

My question is simply is this arrangement of annotations correct? or is there a better way of doing it?

Answer 1

Could you add the DetailsPrimaryKey mapping also ?

What seems strange in your mapping is that you are mapping twice the 'master_pk_1' column in the details tale. By adding the insertable=false option, now inserting works, but i guess updates still not works (in fact when you map columns more than once in an entity you must annotate all but one of them with insertable=false, updatable=false)

To correct that, i think you should move the @ManyToOne Master to the detail id (removing the insertable=false option).

You should also add the option mappedBy="detailsPrimaryKey.master" to the @OneToMany annotation, and maybe also a cascade if you wish the childs to be automatically saved.

(look at http://beavercreekconsulting.com/blog/2008/10/hibernate-annotations-for-a-one-to-many-mapping/ you will see a code solving something quite similar to your problem)