An easy one for most:

I have the following mapping files:

The parent is called Instance.hbm.xml

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">

<hibernate-mapping package="com.ctlm.persistence.hibernatemapping">
<class name="com.blah.blah.instance.Instance"
table="in_instance">

<id name="MIdentifier" column="instanceid#">
<generator class="assigned"/>
</id>

<property name="_mState" column="STATE"></property>
<one-to-one name="_theCreditHolder" class="com.blah.blah.instance.Person"/>
</class>


</hibernate-mapping>

and a child called Person.hbm.xml:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC
"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.blah.persistence.hibernatemapping">

<class name="com.blah.blah.instance.Person" table="IN_PERSON" check="id in ('1', '2', '3')">
<composite-id mapped="true">
<key-property name="_instanceId" column="INSTANCEID#"/>
<key-property name="id" column="PERSONID#"/>
</composite-id>
<property name="_mAcademicTitle" column="P_ACADEMICTITLE" type="java.lang.String"/>
<property name="_mBirthDate" column="P_BIRTHDATE" type="Date" />
<property name="_mBirthLand" column="P_BIRTHLAND" type="java.lang.String"/>

</class>
</hibernate-mapping>

I have had the Instance file working, taking data in and out of the database, but when I add the Person one-to-one property it fails with an error: Caused by: org.hibernate.MappingException: invalid join columns for association

I figure it has something to do with the way I am mapping the id. Basically (I am working with both a legacy application and database), I have a primary key in the Instance table of instanceid# and a composite key in the Person table of instanceid# and personid#.

Can anyone help?