Question

I am trying to use Hibernate to do save/load objects that look like this (these are outlines; I left off the accessors for brevity), but cannot figure out what to place into Item.hbm.xml:

class Item {
  String name;
  Vec3d position;
}

class Vec3d {
  double x;
  double y;
  double z;
}

Database schema:

create table item (
  item_id bigint primary key,
  name varchar(64) not null,
  x double not null,
  y double not null,
  z double not null
);

The Item.hbm.xml basically looks like this so far:

...
<class name="Item" table="item">
  <id name="id" column="item_id">
    <generator class="sequence" />
  </id>

  <property name="name" type="string" />
  <!-- ??? How do I map the position ??? -->
</class>
...

I cannot find documentation on how to get the position vector as a single object, but stored as fields in the same row as the Item class. It seems wasteful to store it in a separate table and incur a join just for reading an Item.

It’s possible that my trouble in finding an answer comes from not knowing the terminology that Hibernate uses for this schema.

Answer 1

This is typically addressed use @Embeddable and @Embedded in hibernate annotations. However, when using a mapping file, you can use the component tag.

http://vuknikolic.wordpress.com/2010/11/27/embeddable-with-hbm-xml/