[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-1134) subclass tag with discriminator in one to many mapping

[Bob Petry (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-1134?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_29475 ] 

Bob Petry commented on HHH-1134:
--------------------------------

Your comment :[The reasoning is that you should not reuse the same FK column for 2 different relationships, which is what is done here.]

is a dificult for me to understand.  

I am facing the same problem, where multiple one to many relationships from PojoA to multiple different subclassed Pojos (PojoC, PojoD, PojoE, where C, D and E are subclasses of PojoB) exist.  

Can you explain to me why a single column (with a foreign key to the ID of PojoA) in the PojoB table that stores my subclassed Pojos, should not be done.

I don't think this is an unreasonable situation.

It seems silly  to have a separate column for each subclass type, where each reference the id of PojoA. 

This seems like a bug to me that would have a simple fix.  It seems like simply performing, an instanceof on each of the SubClass types (until the proper type is identified) rather than casting to the first type that is loaded would solve the issue.

Am I correct or is this issue and the proper solution more convoluted?

> subclass tag with discriminator in one to many mapping
> ------------------------------------------------------
>
>                 Key: HHH-1134
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-1134
>             Project: Hibernate3
>          Issue Type: Bug
>          Components: core
>         Environment: hibernate 3.0.5, Oracle
>            Reporter: Dilip Ranjith
>
> Consider the following hbm.xml file 
> <?xml version="1.0" encoding="UTF-8"?> 
> <!DOCTYPE hibernate-mapping PUBLIC 
>     "-//Hibernate/Hibernate Mapping DTD 3.0//EN" 
>     "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> 
> <hibernate-mapping 
> > 
>     <class 
>         name="DCDTO" 
>         table="ACCDC" 
>         dynamic-update="true" 
>     > 
>         <id 
>             name="ID" 
>             type="java.lang.String" 
>         > 
>                 <column 
>                     name="DCINFOID" 
>                 /> 
>             <generator class="sequence"> 
>                 <param name="sequence">DSEQ</param> 
>               <!-- 
>                   To add non XDoclet generator parameters, create a file named 
>                   hibernate-generator-params-DebtorCreditorDTO.xml 
>                   containing the additional parameters and place it in your merge dir. 
>               --> 
>             </generator> 
>         </id> 
>         <discriminator 
>             column="accountType" 
>             not-null="true" 
>             type="java.lang.String" 
>             force="true" 
>             insert="true" 
>         /> 
>         <property 
>             name="creditMax" 
>             type="java.lang.Double" 
>             update="true" 
>             insert="true" 
>             column="creditMax" 
>         /> 
>  <subclass 
>             name="CDTO" 
>             dynamic-update="true" 
>             dynamic-insert="true" 
>             discriminator-value="C" 
>         > 
> </.subclass> 
>  <subclass 
>             name="DDTO" 
>             dynamic-update="true" 
>             dynamic-insert="true" 
>             discriminator-value="D" 
>         > 
> </.subclass> 
> </class> 
> </hibernate-mapping> 
> DCDTO is the super class while DDTO and CDTO are its child classes 
> If in a mapped object say  TDTO   there are a set of CDTOs and a separate set of DDTOs
> when we get TDTO  the where clause "where  accountType='D'  " is not there when the query for set of DDTOs are generated. so instead of a set of DDTOs i am getting a set of both DDTO's and CDTO's

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