HQL class clause

radu · **Joined:** Wed Jun 15, 2005 4:17 am **Posts:** 156

Hello all,

Is there someone who has used the class clause in a HQL query in NHibernate? Something like this one (taken from the Hibernate docs):

Code:

from eg.Cat cat where cat.class = eg.DomesticCat

While there is no explicit entry in JIRA, it seems that the HQL parser has a bug as it doesn't generate the correct SQL for it. I would like to know if anyone has successfully used the class clause in HQL in NHibernate.

cheers,
radu

michal · **Posted:** Thu Jan 19, 2006 3:46 am

Hi,

I have one query with "class" in where and it performs well. The resulting sql is "where discriminator_column = 'discriminator_value'" (you can't use class if there is no discriminator used)

radu · **Joined:** Wed Jun 15, 2005 4:17 am **Posts:** 156

my class hierarchy uses the table per subclass mapping strategy so there is no discriminator. What I've noticed is that the generated SQL (I'm using SQL Server 2000 dialect) has a slight error in the generated where clause which corresponds for the "class" clause: instead of checking for the class I specified it checks for the base class.

Anyone has used the "class" clause with a class hierarchy mapped with the table per subclass strategy? It seems that I should build a simple test case to prove the bug and submit it to Jira...

cheers,
radu

michal · **Posted:** Thu Jan 19, 2006 2:41 pm

Sorry, but I'm afraid it is not a bug - look at the sentences above mentioned example in the docs :

Quote:

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.

In my opinion (based on the above) the usage of "class" is limited to table-per-class hierarhy strategy, at least in 2.x version of Hibernate (which NH ports)

Somebody please correct me if i'm wrong.