Hibernate：集合的集合

在https://xebia.com/blog/mapping-multimaps-with-
hibernate/
找到了答案

这是11年前的一篇长博客文章。关键代码是：

public class MultiMapType implements UserCollectionType {public boolean contains(Object collection, Object entity) {    return ((MultiMap) collection).containsValue(entity);}public Iterator getElementsIterator(Object collection) {    return ((MultiMap) collection).values().iterator();}public Object indexOf(Object collection, Object entity) {    for (Iterator i = ((MultiMap) collection).entrySet().iterator(); i.hasNext();) {        Map.Entry entry = (Map.Entry) i.next(); Collection value = (Collection) entry.getValue();        if (value.contains(entity)) { return entry.getKey();        }    }    return null;}public Object instantiate() {    return new MultiHashMap();}public PersistentCollection instantiate(SessionImplementor session, CollectionPersister persister) throws HibernateException {    return new PersistentMultiMap(session);}public PersistentCollection wrap(SessionImplementor session, Object collection) {    return new PersistentMultiMap(session, (MultiMap) collection);}public Object replaceElements(Object original, Object target, CollectionPersister persister, Object owner, Map copyCache, SessionImplementor session) throws HibernateException {    MultiMap result = (MultiMap) target;    result.clear();    Iterator iter = ( (java.util.Map) original ).entrySet().iterator();    while ( iter.hasNext() ) {        java.util.Map.Entry me = (java.util.Map.Entry) iter.next();        Object key = persister.getIndexType().replace( me.getKey(), null, session, owner, copyCache );        Collection collection = (Collection) me.getValue();        for (Iterator iterator = collection.iterator(); iterator.hasNext();) { Object value = persister.getElementType().replace( iterator.next(), null, session, owner, copyCache ); result.put(key, value);        }    }    return result;}

}