Selecting only the parent class from HQL

everbright · **Joined:** Wed Jun 15, 2005 2:00 pm **Posts:** 38

Need help with Hibernate? Read this first:
http://www.hibernate.org/ForumMailingli ... AskForHelp

Hibernate version: 3.0.5

Mapping documents:

Code:

<class name="GenericObject" table="GENERIC_OBJECTS" lazy="true" polymorphism="explicit">
      <id name="id" column="id" type="integer" unsaved-value="0">
         <generator class="native" />
      </id>
      <discriminator type="string" column="classID" />
      <property name="classID" column="classID" type="integer" not-null="true" insert="false" update="false"/>
      <property name="name" column="name" type="string" not-null="true" />
      <property name="description" column="description" type="string" />
      <property name="dateCreated" column="dateCreated" type="timestamp" not-null="true" />
      <property name="dateModified" column="dateModified" type="timestamp" />

      <subclass name="User" discriminator-value="1" lazy="false" >
         <join table="GENERIC_USERS">
            <key column="id" />
            <property name="loginName" type="string"/>
            <property name="password" type="string"/>
         </join>
      </subclass>
      
      <subclass name="UserGroup" discriminator-value="2" lazy="false">
         <join table="GENERIC_GROUPS">
            <key column="id" />
            <property name="roleGroup" type="boolean"/>
         </join>
      </subclass>
      
   </class>

Code between sessionFactory.openSession() and session.close():

Code:

Query q = s.createQuery("select g from GenericObject g");
      GenericObject loginName = (GenericObject) q.uniqueResult();

The generated SQL (show_sql=true):

Code:

Hibernate: /* select g from GenericObject g */ select genericobj0_.id as id, genericobj0_.classID as classID0_, genericobj0_.name as name0_, genericobj0_.description as descript4_0_, genericobj0_.dateCreated as dateCrea5_0_, genericobj0_.dateModified as dateModi6_0_, genericobj0_1_.loginName as loginName1_, genericobj0_1_.password as password1_, genericobj0_2_.roleGroup as roleGroup2_, genericobj0_.classID as classID from GENERIC_OBJECTS genericobj0_ left outer join GENERIC_USERS genericobj0_1_ on genericobj0_.id=genericobj0_1_.id left outer join GENERIC_GROUPS genericobj0_2_ on genericobj0_.id=genericobj0_2_.id

Hi all,

As per above, I have a base class, GenericObject, extended by 2 sub-classes User and UserGroup. I've set the polymorphism property for GenericObject to "explicit".

What I thought this would do is that if I executed a HQL like 'from GenericObject g', it should just return me a List of GenericObjects, querying only the GENERIC_OBJECTS table.

However from the generated SQL, it still seems to be doing the joins to the sub-class tables :-(

How do I force Hibernate to just return the GenericObjects, instead of trying to get the specifics of each sub-class? Is it possible to do this at all?

Also, one more other observation:
Can the discriminator type be anything else other than "string"? I'm asking because I've set the type to "integer" initially, but Hibernate complains about this.

Code:

%%%% Error Creating SessionFactory %%%%
org.hibernate.MappingException: Could not format discriminator value to SQL string
   at org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:273)
   at org.hibernate.persister.PersisterFactory.createClassPersister(PersisterFactory.java:55)
   at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:211)
   at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1005)
   at project.hibernate.SessionFactory.currentSession(SessionFactory.java:48)
   at HibernateTest.main(HibernateTest.java:17)
Caused by: java.lang.NumberFormatException: For input string: "project.objects.GenericObject"
   at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
   at java.lang.Integer.parseInt(Integer.java:468)
   at java.lang.Integer.<init>(Integer.java:609)
   at org.hibernate.type.IntegerType.stringToObject(IntegerType.java:53)
   at org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:266)
   ... 5 more
java.lang.NullPointerException
   at project.hibernate.SessionFactory.currentSession(SessionFactory.java:55)
   at HibernateTest.main(HibernateTest.java:17)
Exception in thread "main" 

Thanks in advance for any advice!

alesj · **Posted:** Sun Nov 06, 2005 11:40 am

1. I don't think polymorpihsm="explicit" is meant to be used with subclass or join-class notion. It's more used when you have plain java polymorphism and both classes are simple mapped classes - no other Hibernate biniding between.

2. Sure. You can use few other discriminators. In your case it fails because by default discriminator value is class name - which is ofcourse not integer. Set disciriminator value to your generic object to an integer and it will work.

everbright · **Joined:** Wed Jun 15, 2005 2:00 pm **Posts:** 38

Hi alesj,

Thanks for the suggestions!

Just need some clarifications:

For 1)...
So that means there is actually no way to do what I want to do? Anyway, I've figured a way to do this already:
1. Declare another class which maps to the same table as the root class (GENERIC_OBJECTS) and select that class instead whenever I want to query for generic objects.

That leaves me with the problem of deleting the generic objects cleanly (including the sub-class data).
I think we'll need either a database trigger or a stored procedure for this. Can't really see any other way to do this.

For 2)...
Not sure what you mean, because as I've said, I've originally set the discrimainator-value attribute of the generic object to type "integer". That was what got me the error message in the first place?
And that was why I changed it to "string" instead.

alesj wrote:

1. I don't think polymorpihsm="explicit" is meant to be used with subclass or join-class notion. It's more used when you have plain java polymorphism and both classes are simple mapped classes - no other Hibernate biniding between.

2. Sure. You can use few other discriminators. In your case it fails because by default discriminator value is class name - which is ofcourse not integer. Set disciriminator value to your generic object to an integer and it will work.

hhuber · **Posted:** Mon Nov 07, 2005 2:56 am

everbright wrote:

For 2)...
Not sure what you mean, because as I've said, I've originally set the discrimainator-value attribute of the generic object to type "integer". That was what got me the error message in the first place?
And that was why I changed it to "string" instead.

alesj wrote:

2. Sure. You can use few other discriminators. In your case it fails because by default discriminator value is class name - which is ofcourse not integer. Set disciriminator value to your generic object to an integer and it will work.

I think your original mapping specified the type of the discriminator explicitly:

Code:

I'd let Hibernate find the type from the property itself.
IMHO, if classID is an int or Integer, it should work out automatically if you use the following:

Code:

Alternatively, you might want to specify integer yourself:

Code:

hth,