Composite Primary Key

bitbyter · **Joined:** Thu Dec 01, 2005 12:23 pm **Posts:** 19

Hi there,

I'm wondering if there is a way to create a composite primary key for a database table using Hibernate Annotations, without having to create an @Embeddable primary key class? Or using an "artificial" id as primary key and then only creating a second unique constraint with the two columns!?

For exmaple for the table below I'd like to have "col1" and "col2" as the composite primary key (for whatever reason).

col1 | col2 | col3 | col4 | col5

I was expecting that following annotations would do it...

Code:

@Entity(access=AccessType.FIELD)
@Table(name="MYTABLE")
public MyClass {
  @Id
  private String col1;
  @Id
  private String col2;
  private String col3;
  private String col4;
  private String col5;
}

I should mention that "col1" is a foreign key and points to a primary key of an other table.

Unfortunately this does not work with (Hibernate) annotations. Only "col1" is used as primary key in this case.

I tried several ways but did not find any working solution. Even the way as described in the EJB3.0 specification does not work:

Code:

@Entity(access=FIELD)
@IdClass(com.acme.EmpPK.class)
public class Employee {
   @Id Integer id;
   @Id String name;
   @OneToOne
   @PrimaryKeyJoinColumns({
      @PrimaryKeyJoinColumn(name="ID", referencedColumnName="EMP_ID"), @PrimaryKeyJoinColumn(name="NAME", referencedColumnName="EMP_NAME")})
EmployeeInfo info;
...
}

The annotation @PrimaryKeyJoinColumns is not allowed within a class. And annotating the class with @PrimaryKeyJoinColumns also does not work.

So do I really need an @Embeddable primary key class to use a composite primary key?

Any help/info is appreciated.

- bitbyter

tedberg · **Joined:** Wed Jun 30, 2004 4:02 pm **Posts:** 64

I've always used a many to one with a unique constraint for the foreign key column.

Hibernate itself doesn't work very well with composite keys. Without a 3NF schema you have to use a version column for saveOrUpdate to work. Given that Annotations are not time tested like the xml mappings, I think you are asking for a painful experience trying to do this.

emmanuel · **Posted:** Thu Dec 01, 2005 7:36 pm

For 2. Try

Code:

@OneToOne
@PrimaryKeyJoinColumn
EmployeeInfo info;

For 1. I need to implement that, I'm a bit bored on this :-) Any patch would be welcome.

bitbyter · **Joined:** Thu Dec 01, 2005 12:23 pm **Posts:** 19

emmanuel wrote:

For 2. Try

Code:

@OneToOne
@PrimaryKeyJoinColumn
EmployeeInfo info;

The @PrimaryKeyJoinColumn annotation is not allowed within a class, annotating a class member. It is only allowed to annotate a class itself. At least it does not compile with the Hibernate annotations implementation.

Quote:

For 1. I need to implement that, I'm a bit bored on this :-) Any patch would be welcome.

Gee, unfortunately I currently got no time... and I guess it would take me at least 1-2 days to get into the code. :( Anyway, now at least I know that this is a missing "feature".

- bitbyter

emmanuel · **Posted:** Fri Dec 02, 2005 6:00 am

2. definitely compile. Double check. It's on the unit test suite.
Becareful it's wo the extra s

christian · **Posted:** Fri Dec 02, 2005 6:05 am

[quote]Hibernate itself doesn't work very well with composite keys. Without a 3NF schema you have to use a version column for saveOrUpdate to work. [quote]

You are mistaken.

Erik_G · **Joined:** Fri Aug 25, 2006 4:57 am **Posts:** 4

Does anyone know, if there will be a more comfortable way mapping composite keys? Creating one extra-PK-class works fine, but it is getting ugly when you have a table with a PK consisting of a bigger number of columns.
(I know 'artificial key' is the magic word here but I have to work with a legacy db-scheme...)