<join table="USR_GROUP" fetch="join" optional="true">
        <key property-ref="nonprimary">
            <column name="NAME" />
        </key>
        <many-to-one name="UserGroup" column="USERGROUP" formula="ROLE_ID"
            class="someclass" entity-name="someclass"
            not-null="true">

        </many-to-one>
    </join