Hi all!
This post an issue reporting, not help support.

I'm using Hibernate 3.0.5, and have a class hierarchy like this:
IAccountOwner: top level
Application: extends IAccountOwner and has a bag of accounts
BasicElement: extends IAccountOwner and don't direclty relates to account
Administrator: extends BasicElement and don't direclty relates to account
Member: extends BasicElement and as a one-to-one relation to account.

When I try to load any of the concrete classes (Application, Administrator or Member), all works fine, but, when I try to load an instance of IAccountOwner where the id is an Application (has N accounts), an error occours, saying that more than one records were found with the same id.

I've noticed that it was happening because of the one-to-one relationship between Member to Account. Hibernate tried to load any IAccountOwner using that one-to-one, but Application had multiple accounts. Got it?

That same mapping was working on Hibernate 2.1. I fixed it using fetch="select" on the one-to-one, but, when I load a Member specifically, I would like the fetch to be join. I just think that Hibernate could not assume that one-to-one when loading parent class instances.

Best regards,
Luis.

Hibernate version: 3.0.5

Mapping documents:
<?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 default-lazy="false">

<class name="nl.strohalm.cyclos.entities.accounts.IAccountOwner" table="members" abstract="true">
<id name="id" type="long" column="member_id" unsaved-value="null">
<generator class="native"/>
</id>
<discriminator column="subclass" type="string" force="true"/>

<subclass name="nl.strohalm.cyclos.entities.application.Application" discriminator-value="application">

<bag name="accounts" lazy="false" fetch="select" >
<key column="owner_id"/>
<one-to-many class="nl.strohalm.cyclos.entities.accounts.Account"/>
</bag>

<component name="invoices" class="nl.strohalm.cyclos.entities.accounts.InvoiceList">
<bag name="invoicesList" lazy="true">
<key column="from_account_id"/>
<one-to-many class="nl.strohalm.cyclos.entities.accounts.Invoice"/>
</bag>
</component>
</subclass>

<subclass name="nl.strohalm.cyclos.entities.members.BasicElement" abstract="true">
<property name="postalCode" column="postalCode" type="string"/>
<property name="telephone1" column="telephone1" type="string"/>
<property name="telephone2" column="telephone2" type="string"/>
<property name="email" column="email" type="string"/>
<property name="address" column="address" type="string"/>
<property name="firstName" column="firstName" type="string"/>
<property name="lastName" column="lastName" type="string"/>
<property name="creationDate" column="creationDate" type="calendar"/>

<one-to-one name="user" class="nl.strohalm.cyclos.entities.access.BasicUser" />
<many-to-one name="group" column="group_id" class="nl.strohalm.cyclos.entities.access.Group"/>

<bag name="alertList" lazy="true" cascade="all">
<key column="member"/>
<one-to-many class="nl.strohalm.cyclos.entities.application.alerts.AccountAlert"/>
</bag>

<subclass name="nl.strohalm.cyclos.entities.members.Administrator" discriminator-value="admin">
</subclass>

<subclass name="nl.strohalm.cyclos.entities.members.Member" discriminator-value="member">
<property name="province" column="province" type="string"/>

<property name="hideAddress" column="hideAddress" type="boolean"/>
<property name="hideBirthday" column="hideBirthday" type="boolean"/>
<property name="hideGender" column="hideGender" type="boolean"/>
<property name="hidePostalCode" column="hidePostalCode" type="boolean"/>
<property name="hideTelephone1" column="hideTelephone1" type="boolean"/>
<property name="hideTelephone2" column="hideTelephone2" type="boolean"/>
<property name="hideFax" column="hideFax" type="boolean"/>

<property name="url" column="url" type="string"/>
<property name="fax" column="fax" type="string"/>
<property name="gender" column="gender" type="byte"/>
<property name="birthDay" column="birthDay" type="calendar"/>

<property name="field1" column="field1" type="string"/>
<property name="field2" column="field2" type="string"/>
<property name="field3" column="field3" type="string"/>
<property name="field4" column="field4" type="string"/>
<property name="field5" column="field5" type="string"/>

<many-to-one name="area" column="area_id" class="nl.strohalm.cyclos.entities.application.location.Area"/>
<many-to-one name="businessType" column="businessType_id" class="nl.strohalm.cyclos.entities.members.businessType.BusinessType"/>
<property name="city" column="city" type="string"/>
<many-to-one name="broker" column="broker_id" class="nl.strohalm.cyclos.entities.members.broker.Brokering"/>

<one-to-one name="account" class="nl.strohalm.cyclos.entities.accounts.Account" property-ref="owner" fetch="select"/>

<component name="referenceList" class="nl.strohalm.cyclos.entities.members.references.ReferenceList">
<bag name="given" lazy="true">
<key column="from_member_id"/>
<one-to-many class="nl.strohalm.cyclos.entities.members.references.Reference"/>
</bag>
<bag name="received" lazy="true">
<key column="to_member_id"/>
<one-to-many class="nl.strohalm.cyclos.entities.members.references.Reference"/>
</bag>
</component>

<component name="contactList" class="nl.strohalm.cyclos.entities.members.contacts.ContactList">
<bag name="contacts" lazy="true">
<key column="member_id"/>
<one-to-many class="nl.strohalm.cyclos.entities.members.contacts.Contact"/>
</bag>
</component>

<component name="adsList" class="nl.strohalm.cyclos.entities.members.ads.AdsList">
<bag name="ads" lazy="true">
<key column="member_id"/>
<one-to-many class="nl.strohalm.cyclos.entities.members.ads.Ad"/>
</bag>
</component>

<bag name="moneyContributionsPayed" lazy="true">
<key column="member_id"/>
<one-to-many class="nl.strohalm.cyclos.entities.contributions.MoneyContributionHistory"/>
</bag>

<component name="invoices" class="nl.strohalm.cyclos.entities.accounts.InvoiceList">
<bag name="invoicesList" lazy="true">
<key column="from_account_owner_id"/>
<one-to-many class="nl.strohalm.cyclos.entities.accounts.Invoice"/>
</bag>
</component>

</subclass>

</subclass>

</class>

</hibernate-mapping>


Code between sessionFactory.openSession() and session.close():
Session session = PersistenceFactory.getSession();
try {
try {
System.out.println("AccountOwner");
System.out.println(session.load(IAccountOwner.class, new Long(1)));
} catch (Exception e) {
e.printStackTrace();
}
try {
System.out.println("Application");
System.out.println(session.load(Application.class, new Long(1)));
} catch (Exception e) {
e.printStackTrace();
}
try {
System.out.println("Administrator");
System.out.println(session.load(Administrator.class, new Long(2)));
} catch (Exception e) {
e.printStackTrace();
}
try {
System.out.println("Member");
System.out.println(session.load(Member.class, new Long(3)));
} catch (Exception e) {
e.printStackTrace();
}
} finally {
session.close();
}

Full stack trace of any exception that occurs:
org.hibernate.HibernateException: More than one row with the given identifier was found: 1, for class: nl.strohalm.cyclos.entities.accounts.IAccountOwner
at org.hibernate.loader.entity.EntityLoader.load(EntityLoader.java:137)
at org.hibernate.loader.entity.EntityLoader.load(EntityLoader.java:101)
at org.hibernate.persister.entity.BasicEntityPersister.load(BasicEntityPersister.java:2471)
at org.hibernate.event.def.DefaultLoadEventListener.loadFromDatasource(DefaultLoadEventListener.java:351)
at org.hibernate.event.def.DefaultLoadEventListener.doLoad(DefaultLoadEventListener.java:332)
at org.hibernate.event.def.DefaultLoadEventListener.load(DefaultLoadEventListener.java:113)
at org.hibernate.event.def.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:151)
at org.hibernate.event.def.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:79)
at org.hibernate.impl.SessionImpl.load(SessionImpl.java:603)
at org.hibernate.impl.SessionImpl.load(SessionImpl.java:596)
at nl.strohalm.cyclos.Main.main(Main.java:56)

Name and version of the database you are using:
MySQL 4.1

The generated SQL (show_sql=true):
select iaccountow0_.member_id as member1_8_, iaccountow0_.postalCode as postalCode14_8_, iaccountow0_.telephone1 as telephone4_14_8_, iaccountow0_.telephone2 as telephone5_14_8_, iaccountow0_.email as email14_8_, iaccountow0_.address as address14_8_, iaccountow0_.firstName as firstName14_8_, iaccountow0_.lastName as lastName14_8_, iaccountow0_.creationDate as creatio10_14_8_, iaccountow0_.group_id as group11_14_8_, iaccountow0_.province as province14_8_, iaccountow0_.hideAddress as hideAdd13_14_8_, iaccountow0_.hideBirthday as hideBir14_14_8_, iaccountow0_.hideGender as hideGender14_8_, iaccountow0_.hidePostalCode as hidePos16_14_8_, iaccountow0_.hideTelephone1 as hideTel17_14_8_, iaccountow0_.hideTelephone2 as hideTel18_14_8_, iaccountow0_.hideFax as hideFax14_8_, iaccountow0_.url as url14_8_, iaccountow0_.fax as fax14_8_, iaccountow0_.gender as gender14_8_, iaccountow0_.birthDay as birthDay14_8_, iaccountow0_.field1 as field24_14_8_, iaccountow0_.field2 as field25_14_8_, iaccountow0_.field3 as field26_14_8_, iaccountow0_.field4 as field27_14_8_, iaccountow0_.field5 as field28_14_8_, iaccountow0_.area_id as area29_14_8_, iaccountow0_.businessType_id as busines30_14_8_, iaccountow0_.city as city14_8_, iaccountow0_.broker_id as broker32_14_8_, iaccountow0_.subclass as subclass8_, basicuser1_.user_id as user1_0_, basicuser1_.password as password18_0_, basicuser1_.userName as userName18_0_, basicuser1_.lastLogin as lastLogin18_0_, basicuser1_.subclass as subclass0_, group2_.group_id as group1_1_, group2_.name as name11_1_, group2_.description as descript4_11_1_, group2_.subclass as subclass1_, area3_.area_id as area1_2_, area3_.name as name19_2_, businessty4_.businessType_id as business1_3_, businessty4_.name as name20_3_, brokering5_.brokering_id as brokering1_4_, brokering5_.broker_id as broker2_21_4_, brokering5_.brokered_id as brokered3_21_4_, brokering5_.note as note21_4_, brokering5_.commissionDate as commissi5_21_4_, member6_.member_id as member1_5_, member6_.postalCode as postalCode14_5_, member6_.telephone1 as telephone4_14_5_, member6_.telephone2 as telephone5_14_5_, member6_.email as email14_5_, member6_.address as address14_5_, member6_.firstName as firstName14_5_, member6_.lastName as lastName14_5_, member6_.creationDate as creatio10_14_5_, member6_.group_id as group11_14_5_, member6_.province as province14_5_, member6_.hideAddress as hideAdd13_14_5_, member6_.hideBirthday as hideBir14_14_5_, member6_.hideGender as hideGender14_5_, member6_.hidePostalCode as hidePos16_14_5_, member6_.hideTelephone1 as hideTel17_14_5_, member6_.hideTelephone2 as hideTel18_14_5_, member6_.hideFax as hideFax14_5_, member6_.url as url14_5_, member6_.fax as fax14_5_, member6_.gender as gender14_5_, member6_.birthDay as birthDay14_5_, member6_.field1 as field24_14_5_, member6_.field2 as field25_14_5_, member6_.field3 as field26_14_5_, member6_.field4 as field27_14_5_, member6_.field5 as field28_14_5_, member6_.area_id as area29_14_5_, member6_.businessType_id as busines30_14_5_, member6_.city as city14_5_, member6_.broker_id as broker32_14_5_, member7_.member_id as member1_6_, member7_.postalCode as postalCode14_6_, member7_.telephone1 as telephone4_14_6_, member7_.telephone2 as telephone5_14_6_, member7_.email as email14_6_, member7_.address as address14_6_, member7_.firstName as firstName14_6_, member7_.lastName as lastName14_6_, member7_.creationDate as creatio10_14_6_, member7_.group_id as group11_14_6_, member7_.province as province14_6_, member7_.hideAddress as hideAdd13_14_6_, member7_.hideBirthday as hideBir14_14_6_, member7_.hideGender as hideGender14_6_, member7_.hidePostalCode as hidePos16_14_6_, member7_.hideTelephone1 as hideTel17_14_6_, member7_.hideTelephone2 as hideTel18_14_6_, member7_.hideFax as hideFax14_6_, member7_.url as url14_6_, member7_.fax as fax14_6_, member7_.gender as gender14_6_, member7_.birthDay as birthDay14_6_, member7_.field1 as field24_14_6_, member7_.field2 as field25_14_6_, member7_.field3 as field26_14_6_, member7_.field4 as field27_14_6_, member7_.field5 as field28_14_6_, member7_.area_id as area29_14_6_, member7_.businessType_id as busines30_14_6_, member7_.city as city14_6_, member7_.broker_id as broker32_14_6_, account8_.account_id as account1_7_, account8_.creationDate as creation3_2_7_, account8_.ownerName as ownerName2_7_, account8_.owner_id as owner5_2_7_, account8_.credit_limit as credit6_2_7_, account8_.subclass as subclass7_ from members iaccountow0_ left outer join users basicuser1_ on iaccountow0_.member_id=basicuser1_.user_id left outer join groups group2_ on iaccountow0_.group_id=group2_.group_id left outer join areas area3_ on iaccountow0_.area_id=area3_.area_id left outer join businessTypes businessty4_ on iaccountow0_.businessType_id=businessty4_.businessType_id left outer join brokering brokering5_ on iaccountow0_.broker_id=brokering5_.brokering_id left outer join members member6_ on brokering5_.broker_id=member6_.member_id left outer join members member7_ on brokering5_.brokered_id=member7_.member_id left outer join accounts account8_ on iaccountow0_.member_id=account8_.owner_id and account8_.subclass in ('account', 'limited_account') where iaccountow0_.member_id=? and iaccountow0_.subclass in ('admin', 'member', 'application')


Debug level Hibernate log excerpt: