How do I add a composite index to NHibernate mapping?

See more:

NHibernate

Hi Guys,

I'm trying to add a composite index to the NHibernate mapping file so I do something like:

<composite-index class="PossibleResource">
    <key-property  name="Operation_id"/>
    <key-property  name="Resource_id"/>
</composite-index>

But then, when I try to generate the DB I'm getting the following error:

The element 'class' in namespace 'urn:nhibernate-mapping-2.2' has invalid child element 'composite-index' in namespace 'urn:nhibernate-mapping-2.2'. List of possible elements expected: 'property, many-to-one, one-to-one, component, dynamic-component, properties, any, map, set, list, bag, idbag, array, primitive-array, join, subclass, joined-subclass, union-subclass, loader, sql-insert, sql-update, sql-delete, filter, resultset, query, sql-query' in namespace 'urn:nhibernate-mapping-2.2'.


What is the best practice to create a composite index in NHibernate?

Thanks,
Shai