[INTERESTING] How to map a multilevel inheritanche hierarchy

neomario · **Joined:** Sat Oct 06, 2007 9:44 am **Posts:** 3

Hi!
I would like to know how to map a multilevel inheritance hieararchy.
I have:

1) Superclass A
2) Class B,C extends A
3) Class D,E extends B

In another mapping, I have a many-to-one relationship with class B.
How can I map this?

pavol.zibrita · **Joined:** Sun Sep 30, 2007 7:51 pm **Posts:** 93

Where is the problem?

Pavol

neomario · **Joined:** Sat Oct 06, 2007 9:44 am **Posts:** 3

Hi Pavol.
There is no problem if I use a table per subclass strategy, with joined-subclass. But there is a legacy mapping for the first level of hierarchy using subclass with discriminator.
Now, if the discriminator for Class B is "CLASSB" and the discriminators for class D and E are "CLASSD" and "CLASSE", can I do polymorphic queries? Can I query for Class B objects and get both Class D and Class E objects?
This is the problem. I can't change the original mapping.

Mario

pavol.zibrita · **Joined:** Sun Sep 30, 2007 7:51 pm **Posts:** 93

HI!

Yes, I think the polymorphic query will work, unless you will specify in entity polymorphicType explicit.

Pavol

neomario · **Joined:** Sat Oct 06, 2007 9:44 am **Posts:** 3

Thank you, I will try!

nalla_vinay · **Posted:** Thu Sep 25, 2008 3:21 am

Hi,

I have similar problem with multi level inheritance:

I have table like:

Code:

Table: Test_Comments
comment_id varchar2(15),
entity_id varchar2(15),
entity_type_cd varchar2(32),
field_cd varchar2(32),
field_value varchar2(2000).

Here we moved all comments to a separate table for all remaining entities.
entit_id is the corresponsind entity for which this comment belongs to and the entity_type_cd is the discriminator for distinguishing the type of entity and field_cd is the discriminator within the entity to distinguish the field.

so the class hierarchy is :

Code:

Class TestComments{
String commendId;
String fieldValue;

}

(entity_type_cd is the discriminator value=XYZ)
Class XyzTestComment extends TestComments{
Xyz entityId;
}
(field_cd is the discriminator value=FIELD1)
Class XyzField1TestComment extends XyzTestComment{
}
(field_cd is the discriminator value=FIELD2)
Class XyzField2TestComment extends XyzTestComment{
}
(entity_type_cd is the discriminator value=XXX)
Class XxxTestComment extends TestComments{
Xxx entityId;
} 
(field_cd is the discriminator value=FIELD)
Class XxxFieldTestComment extends XxxTestComment{
}

Mapping file i'm trying to write is:

Code:

<hibernate-mapping>
    <class name="com.model.TestComments" table="testComments" schema="GL_PA_NEW_TEST">
        <id name="commentId" type="string">
            <column name="commentId" length="15" />

            <generator class="sequence">
               <param name="sequence">GL_PA_SEQ</param>
            </generator>
        </id>
        
        <discriminator force="true" type="string">
           <column name="entity_type_cd" length="20" />
        </discriminator>
        
   
        <subclass name="com.model.XyzTestComment" discriminator-value="XYZ">

how can I subclass it further based on field_cd, i am unable to write <discriminator > here

Code:

           <many-to-one name="entityId" class="com.model.Xyz">
         <column name="entityId" length="15" not-null="true" />
      </many-to-one> 
        
        </subclass>
................... same problem with XXX discriminator value.
       
    </class>
</hibernate-mapping>

Please suggest me how to map this relation.. please tell me what is polymorphic query where can i get more information on that.

damnhandy · **Posted:** Sun Sep 28, 2008 1:15 pm

This can be a bitch :) However, if you need to have the deeper specialization's utilize two columns rather than one, you may want to look at using a formula for the discriminator rather than a single column. This will allow you to create a SQL fragment that you can use to determine when the subclass is used.

Ryan-

nalla_vinay · **Posted:** Mon Sep 29, 2008 8:40 am

Thanks Ryan for your reply, I have removed multiple discriminators and concatenated them at the column level to solve this problem. However still i've a doubt how to use nested <subclass> will that be used to solve multilevel inheritance problem? If you have any resources to make use of nested <subclass> please share with me.

Thanks in advance.

nalla_vinay · **Posted:** Fri Dec 12, 2008 6:12 am

Hi,

I have few doubts on inheritance.

Code:

ClassA {

String id;
List<ClassB> childs;
ClassAComment classAcomment;

}

ClassB{
String id;
ClassBComment classBcomment;
}

I would like to store the field values which are having >500 size in TestComments.

TestComment:

Code:

COMMENT_ID          PK
PARENT_ENTITY_ID not null
ENTITY_ID              not null
ENTITY_FIELD_CD   not null
fieldValue

at the database level i don't have any foriegn key constraint on parentId and entityId, but i am trying to enforce them at hibernate mapping level like:

Code:

ClassA mapping:

<class name="ClassA" table="TableA">
      <id name="id" type="string">
         <column name="TABLEA_ID" length="15" />

         <generator class="sequence">
            <param name="sequence">TEST_SEQ</param>
         </generator>
      </id>
      
      <one-to-one name="classAcomment"
         class="ClassAComment"
         cascade="all" property-ref="entityId" />
         
       <bag name="childs" inverse="true" cascade="all">
            <key>
                <column name="TABLEA_ID" length="15" not-null="true" />
            </key>

            <one-to-many class="ClassB" />
        </bag>
      
</class>

ClassB mapping:

<class name="ClassB" table="TableB">
      <id name="id" type="string">
         <column name="TABLEB_ID" length="15" />

         <generator class="sequence">
            <param name="sequence">TEST_SEQ</param>
         </generator>
      </id>
      
      <one-to-one name="classBcomment"
         class="ClassABomment"
         cascade="all" property-ref="entityId" />
         
       <many-to-one name="classA" class="ClassA" fetch="select">
            <column name="TABLEA_ID" length="15" not-null="true" />
        </many-to-one>
      
</class>

TestComments mapping:
      
<class name="TestComment"
      table="O_TEST_COMMENT">
      <id name="commentId " type="string">
         <column name="COMMENT_ID" length="15" />

         <generator class="sequence">
            <param name="sequence">TEST_SEQ</param>
         </generator>
      </id>

      <discriminator force="true" type="string">
         <column name="ENTITY_FIELD_CD" length="32" not-null="true" />
      </discriminator>

<subclass name="ClassAComment"
         discriminator-value="CLASSA_COMMENT">

    
         <many-to-one name="parentEntityId"
            class="ClassA" lazy="false">
            <column name="PARENT_ENTITY_ID" length="15"
               not-null="true" />               
         </many-to-one>
         
         <many-to-one name="entityId"
            class="ClassA" lazy="false">
            <column name="ENTITY_ID" length="15"
               not-null="true" />               
         </many-to-one>         
         
      </subclass>

      <subclass
         name="ClassBComment"
         discriminator-value="CLASSB_COMMENT">
         
         <many-to-one name="parentEntityId"
            class="ClassA" lazy="false">
            <column name="PARENT_ENTITY_ID" length="15"
               not-null="true" />
         </many-to-one>
         
         <many-to-one name="entityId"
            class="ClassB" lazy="false">
            <column name="ENTITY_ID" length="15"
               not-null="true" />               
         </many-to-one>
      </subclass>

.......
</class>

I am duplicating one selected ClassA object along with its child by setting Id to null and tried merge on ClassA, the queries generated in the following order:

first insert on ClassA
insert on ClassAComment
insert on ClassBComment (here i am getting exception)

Hibernate is trying to insert child(ClassBComment) first before Parent(ClassB), is there any way to tell hibernate to insert parent first.

caused by: org.hibernate.PropertyValueException: not-null property references a null or transient value: com.test.domain.ClassBComment.entityId
at org.hibernate.engine.Nullability.checkNullability(Nullability.java:72)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:290)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:181)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:94)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:507)
at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:499)
at org.hibernate.engine.CascadingAction$5.cascade(CascadingAction.java:218)
at org.hibernate.engine.Cascade.cascadeToOne(Cascade.java:268)
at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:216)
at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:169)
at org.hibernate.engine.Cascade.cascadeCollectionElements(Cascade.java:296)
at org.hibernate.engine.Cascade.cascadeCollection(Cascade.java:242)
at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:219)
at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:169)
at org.hibernate.engine.Cascade.cascade(Cascade.java:130)
at org.hibernate.event.def.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:456)
at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:334)
at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:181)
at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:121)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:187)
at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:33)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:172)
at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:27)
at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:70)
at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:535)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:523)
at org.hibernate.impl.SessionImpl.save(SessionImpl.java:519)
at org.springframework.orm.hibernate3.HibernateTemplate$12.doInHibernate(HibernateTemplate.java:693)
at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:419)
... 120 more