Question

I am currently trying to create two simple one-to-one mappings using Hibernate but somehow it doesn’t work as I want it to.

My primary class is called MailAccount and its mapping looks like this:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
<!-- Generated 26.04.2011 14:49:15 by Hibernate Tools 3.3.0.GA -->
<hibernate-mapping package="test.account">
    <class name="MailAccount" table="MAILACCOUNTS" dynamic-update="true">

        <id name="id" column="MAIL_ACCOUNT_ID">
            <generator class="native" />
        </id>

        <one-to-one name="incomingServer" cascade="all" />

        <one-to-one name="outgoingServer" cascade="all" />

    </class>
</hibernate-mapping>

The server mapping file looks like this:

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<!-- Generated 02.05.2011 12:32:52 by Hibernate Tools 3.3.0.GA -->
<hibernate-mapping>
    <class name="test.server.MailServer" table="MAILSERVER">

        <id name="id" type="long" access="field">
            <column name="MAIL_SERVER_ID" />
            <generator class="native" />
        </id>

        <one-to-one name="mailAccount" class="test.account.MailAccount" foreign-key="MAIL_SERVER_ID"></one-to-one>

    </class>
</hibernate-mapping>

Now, if I let Hibernate create the tables, I get pretty much that what I want: A table “MailAccount” with the column “MAIL_ACCOUNT_ID” and another table “MailServer” also with a column for the id.

If I call session.save(mailAccountInstance);, Hibernate correctly saves the data to the tables.

BUT once I try to load the data into a MailAccount instance, Hibernate only loads the “incomingServer” property into a new MailAccount instance and the outgoingServer property is empty.

I also don’t understand how Hibernate joins both tables together since the table “MailServer” doesn’t save the id of the MailAccount each server belongs to as a foreign key.

How can I fix this?

Thanks in advance!

Ps: I am pretty new to Hibernate, so don’t beat me up to much for obvious mistakes 🙂

Answer 1

I suggest taking a look at the Association Mappings chapter in the Hibernate reference manual. For a bidirectional one-to-one mapping, it’s suggested to use a <one-to-one> on one end and <many-to-one unique="true"> on the other end.