Date: Sun, 07 Aug 2011 21:38:25 +1000
From: Lionel <lionelv@none.com>
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Subject: Hibernate foreign key as primary key
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This may be a little off topic but I'm sure there are some experts in here.

I'm having some troubles getting using a foreign key as a primary key. 
In this post I will use the most simple issue I'm having trouble with.

Here's some snippets (pharmacy project):

public abstract class AbstractDrugModel
{
     private String name;
     private IntravascularDrug ivDrug;
}

public class IntravascularDrug
{
     private AbstractDrugModel drug;
}

Note 1: I am only just introducing hibernate, previously I did the 
databases manually and in that scenario IntravascularDrug did not 
contain an AbstractDrugModel instance.

Note 2: ivDrug can be null.

In my mapping files I have (at this point in time, I've tried other 
approaches):

<hibernate-mapping>
   <class
     lazy="false"
     name="tciworks.drugmodel.IntravascularDrug"
     table="IntravascularDrug">
     <composite-id>
       <key-many-to-one name="drug" column="DrugName"/>
     </composite-id>
     ...
     </class>
</hibernate-mapping>

<hibernate-mapping>
   <class
     dynamic-insert="false"
     dynamic-update="false"
     lazy="false"
     mutable="true"
     name="tciworks.drugmodel.AbstractDrugModel"
     optimistic-lock="version"
     polymorphism="implicit"
     select-before-update="false"
     table="Drug">

     <id column="Name" name="name"/>
     <discriminator column="DrugModelType"/>
     ...
     <many-to-one
       cascade="all"
       column="DrugName"
       name="intravascularDrug"
       not-null="false"
       unique="true"/>

     <subclass
       discriminator-value="USER_DEFINED"
       name="tciworks.drugmodel.userdefined.UserDefinedDrugModel"/>
   </class>
</hibernate-mapping>

This example includes only one concrete sub-class of AbstractDrugModel, 
there are others. Drug name is unique hence being used as PK.

When I have Hibernate create the database tables everything appears 
fine, but on save, it seems to be saving IntravascularDrug first and 
hence gives the following error:

Sun Aug 07 21:03:25 EST 2011: ERROR  logExceptions, Cannot add or update 
a child row: a foreign key constraint fails 
(`tciworkssqlextension`.`intravasculardrug`, CONSTRAINT 
`FK19E96D413937CB47` FOREIGN KEY (`DrugName`) REFERENCES `drug` (`Name`))

Does anyone have any suggestions on how I should do this?

Thanks

Lionel.