Grails: domain class mapping (collection of hibernate user types)

I am wondering if is possible to implement following domain model.

Let's have a domain class which contains set of intervals (joda time). I can use org.joda.time.contrib.hibernate.PersistentInterval hibernate user type for mapping of Interval to database table (by similar way as in http://www.grails.org/JodaTime+Plugin). However I cannot figure out how to implement mapping if I have set of intervals, not only one interval.

Example:

class Activity {  
   ...    
   Set intervals = []  
   ...  
   static hasMany = [    
       intervals: org.joda.time.Interval  
   ]  

   // This is incorrect implementation, I have set of intervals  
   // and this would be correct if I had only one interval  
   // How to implement mapping in this case?  
   static mapping = {  
       intervals type: PersistentInterval, {  
           column name: "start"  
           column name: "end"  
       }  
   }  

}

Implementation above fails with following error:

2010-10-23 18:开发者_JS百科30:25,483 [main] ERROR context.GrailsContextLoader - Error executing bootstraps: Error creating bean with name 'messageSource': Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting bean property 'sessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory': Invocation of init method failed; nested exception is org.hibernate.MappingException: Foreign key (FK4FDC5B1E5107CA0:activity_intervals [start,end])) must have same number of columns as the referenced primary key (activity [id]) org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'messageSource': Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'transactionManager': Cannot resolve reference to bean 'sessionFactory' while setting bean property 'sessionFactory'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sessionFactory': Invocation of init method failed; nested exception is org.hibernate.MappingException: Foreign key (FK4FDC5B1E5107CA0:activity_intervals [start,end])) must have same number of columns as the referenced primary key (activity [id]) at org.grails.tomcat.TomcatServer.start(TomcatServer.groovy:212)

I thought that work-around of this issue is to extract Interval to separate domain class extending Interval and specify mapping within it. However, Interval is final class so extending is not possible.

Thanks for your advices.

I am replying my own question, maybe this answer will be useful for someone.

Until now I have found only one way how to implement given model - by Hibernate XML mapping files:

<hibernate-mapping package="mappingtest">  
    <class name="Activity">  
        <id name="id">  
            <generator class="native"/>  
        </id>  
        <set name="intervals">  
            <key column="activity_id" not-null="true"/>  
            <element type="org.joda.time.contrib.hibernate.PersistentInterval">  
                <column name="startDate"/>  
                <column name="endDate"/>  
            </element>  
        </set>  
    </class>  
</hibernate-mapping>  

and domain class implementation:

class Activity {    
    Long id    
    Set intervals = []

    static constraints = {
    }
}

I also had to move domain class from grails-app/domain to src/groovy directory, otherwise application running failed with (grails-1.3.5):

...
org.hibernate.DuplicateMappingException: Duplicate class/entity mapping mappingtest.Activity
...

Second problem with above implementation I have discovered is that when I turned on scaffolding (for testing purpose) by:

class ActivityController {
    static scaffold = true
    ...
}

showing of created activity failed with error:

Exception Message: No such property: id for class: org.joda.time.Interval Possible solutions: end Caused by: Error evaluating expression [i.id] on line [38]: No such property: id for class: org.joda.time.Interval Possible solutions: end

but manual implementation of getting activities from DB and its showing worked.

Edit: additionally I found solution of scaffolding and DuplicateMappingException issues. They were caused by invalid location of Activity.hbm.xml - package directory structure was missing. Correct location is grails-app/conf/hibernate/mappingtest/Activity.hbm.xml.