You can also specify that a repository item property is a collection of repository items. In the previous example, an author may have written more than one book. Instead of the book property in the preceding example, this next example uses a books_written property whose value is a Set of book repository items. The <property> tag for the books_written property uses the following attributes:
data-type="set", to specify that the property value is aSetof itemscomponent-item-type="book", to specify that the items making up the set are items of thebookitem descriptorcolumn-name="book_id", to specify that the database column is namedbook_id, rather thanbooks_written.
<!-- 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" item-type="author" column-name="author_id"/> </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="city"/> <property name="state"/> <property name="zip"/> </table> <table name="book" id-column-names="author_id" type="multi"> <property name="books_written" data-type="set" component-item-type="book" column-name="book_id"/> </table> </item-descriptor>
Note that in this example, the book table is defined twice in the XML, first in the book item descriptor and then in the author item descriptor. The second time, this table is a multi-table where each author item may have more than one row with the id column. In a multi-table, all of the attributes that we define are multi-valued types. To define Array, List and Map types, you also must specify a multi-column-name attribute on the table tag. This specifies which column is to be used as the sorting value to determine the order of the List and the key for the Map.
Now the properties author and books_written are actually real beans (in this case RepositoryItems) instead of just simple Java primitives. In the author item descriptor, the books_written property is a Set of RepositoryItems that correspond to books. The other types supported are List, Map, and Array.
