CODEWITHSUNDEEP
javaoophibernatehqlhibernate-mapping
javagirl
javagirl

Reputation: 1675

How to add property counted in DB to @Entity class?

I have an Entity. And sometimes I need this object also contains some value, call it 'depth'. The query may look like 'select b.id, b.name, b..., count(c.id) as depth from Entity b, CEntity c where ...'. So I've created class NonHibernateEntity which extends Entity. And then results of query written above are perfectly stored as List of NonHibEntity, which consists of all the fields of Entity (as they are extended), and property 'depth'. I make it by setting aliasToBean results transformer: .setResultTransformer(Transformers.aliasToBean(NHEntity.class)). But, it is annoying and inconvenient - to specify all the aliases of all the needed fields. And then, if I want to save one of this object to DB - session.saveOrUpdate((Enity)nHibEntity) - there are an exception about nHibEntity isn't Hibernate Entity.

I heard about storing 'entity' as field in NonHibEntity (aggregation, not inheritance). But it seems this is rather inconvenient too. What do you think? What is an appropriate solution?

Upvotes: 3

Views: 479

Answers (2)

javagirl
javagirl

Reputation: 1675

If somebody want to know - I solved this problem in such way:

just made this calculated field as @Transient, and then 

List<BaseEntry> result = new ArrayList<BaseEntry>();
    Iterator it =  session()
    .createQuery("select b, (select count(p.id) as depth from BaseEntry p " +
            "   where ... ) as d" +
            " from BaseEntry b " +
            " where ... ")
    .list().iterator();
    while ( it.hasNext() ) {
        Object[] row = (Object[]) it.next();
        BaseEntry entry = (BaseEntry) row[0];
        Long d = (Long) row[1];
        entry.setD(d);
        result.add(entry);
    }
    return result;

It works good, and seems that it can be easily supported in future

Upvotes: 0

Don Roby
Don Roby

Reputation: 41137

A Formula column mapping may be suitable for your needs. I would try this first.

If this causes performance issues as you fear, you might try a mapped class hierarchy with this field only in the child, and mapping both to the same table. Not sure this will actually work though...

As a last resort, do what you've got now using a non-mapped class, but with the entity as a field in your other class - aggregation instead of inheritance as you say, and make sure there's a way of retrieving the mapped entity from the unmapped one so that you can save. It be sensible to make it a Decorator, so that it's both a subclass and aggregate and you can continue to ignore the distinction in much of your code.

With the non-mapped subclass and/or aggregate, however, you'll have to pull out the entity in order to save.

Upvotes: 1

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