The value of a property of a repository item can be another repository item. Both multi-valued properties and single-valued properties can have repository items as property values. This is a powerful feature, and allows you much greater flexibility in defining a database schema that your application accesses as a repository.

Consider as a simple example a repository that contains books and authors. You can represent both books and authors as repository items, which enables you to do things like this:

Repository gsa = ...;
String myBookId = ...;

// get my book from the db
RepositoryItem book = gsa.getItem(myBookId,descriptorName);

// get the author of my book (it's a dynamic bean too!)
RepositoryItem author = (RepositoryItem)book.getPropertyValue("author");

Without support for objects as properties, the application must get an authorId from the book and perform another lookup to get the actual author.

You can specify that a repository item property is another repository item, rather than a primitive, with the item-type attribute instead of the data-type attribute. The following example shows a portion of a template that defines two item descriptors, book and author:

<!-- The "book" item type -->
<item-descriptor name="book" default="true">
  <table name="book" type="primary" id-column-names="book_id">
    <property name="title"/>
    <property name="author" column-name="author_id"
              item-type="author"/>
  </table>
</item-descriptor>

<!-- The "author" item type -->
<item-descriptor name="author">
  <table name="author" id-column-names="author_id" type="primary">
    <property name="lastName"/>
    <property name="firstName"/>
  </table>
  <table name="book" id-column-names="author_id" type="auxiliary">
    <property name="book" item-type="book" column-name="book_id"/>
  </table>
</item-descriptor>