Criteria API and polymorphic queries

dyn · **Joined:** Wed Aug 27, 2003 7:53 am **Posts:** 27

I have the following [sub]class structure: A <- B <- C (where B is a superclass of C and a child class of A), with discriminator values 'a', 'b' and 'c' accordingly, and using explicit polymorphism. I'm trying to do queries which only return instances of the needed class, no subclasses. Using the query language, I have zero problems doing so, but trying to use the Criteria API showed some interesting results.

Sample code:

Code:

criteria = session.createCriteria(B.class); 
criteria.add(Expression.eq("class", "b"));
criteria.list();

generates SQL having this where clause (watching from P6Spy):

Code:

where this.doctype='b' and this.doctype in ('c', 'b')

..where doctype of course is the name of the discriminator column. Ok, the above works, but looks dirty enough to let me ask whether I'm doing it the right way here..

Some history: first I tried to assign B.class to the criteria, which gave a classcastexception - the Hibernate source clearly showed it was trying to cast it to a string. Then I tried to provide the full class name, which got inserted directly in the SQL above, so I *guess* I'd need to specify the actual discriminator value there.. am I right?

thanks,
dyn

ps. trying to find a similar issue here on the forums, I've bumped into the following q&a: http://forum.hibernate.org/viewtopic.php?t=927708&highlight=criteria+polymorphic, and I really wonder how I can set explicit polimorphism to a subclass, as the DTD only specifies polymorphism=[explicit|implicit] to the 'class' tag, but not for 'subclass'..

tcollins · **Posted:** Wed Feb 25, 2004 4:42 pm

I have done something like this...

User is the superclass to many classes.

User (parent)
--- Administrator (child)
--- AccountManager (child)
--- FinanceAdministrator (child)

Code:

StringBuffer sb = new StringBuffer(50);
sb.append("from com.blah.User user ");
sb.append("where user.class = com.blah.Administrator ");
sb.append("or user.class = com.blah.AccountManager ");
sb.append("or user.class = com.blah.FinanceAdministrator ");
sb.append("order by user.class, user.firstName");
Query query = session.createQuery(sb.toString());

Check out 10.7 in the docs... http://www.hibernate.org/hib_docs/reference/html/query-language.html#query-language-s5

Likewise, the special property class accesses the discriminator value of an instance in the case of polymorphic persistence. A Java class name embedded in the where clause will be translated to its discriminator value.
from eg.Cat cat where cat.class = eg.DomesticCat

dyn · **Joined:** Wed Aug 27, 2003 7:53 am **Posts:** 27

Collins, that's correct so far.. but I'd like to reach the same effect using the new Criteria API, not standard hql.[/quote]

emmanuel · **Posted:** Thu Feb 26, 2004 7:03 am

I don't think this is doable. Check JIRA on such subjects

dyn · **Joined:** Wed Aug 27, 2003 7:53 am **Posts:** 27

Couldn't find anything like that in JIRA. Do you guys plan to do it, may I put this as a feature request there?

emmanuel · **Posted:** Mon Mar 01, 2004 12:42 pm

Yes into JIRA

dyn · **Joined:** Wed Aug 27, 2003 7:53 am **Posts:** 27

HB-768

Thanks in advance!

dyn · **Joined:** Wed Aug 27, 2003 7:53 am **Posts:** 27

Gavin's comment in JIRA:

Quote:

Ah this doesn't bother me. -1 to complexifying the codebase for this.

Ok, I understand, that's your decision ofc :) The one fact I don't understand is, that if you push the new (and lovely!) Criteria API that much, and as you're so proud how polymorphism work with Hibernate and if polymorphism with Criteria already works (see my original comment!), just doesn't generate the cleanest possible SQL, then what's the point about complexifying the codebase.. Maybe I should have posted to JIRA as a minor fix, not as an improvement, or feature?

Anyway, sorry if I felt pushy above, and keep up the good work with Hibernate! :)

dyn