Question

I got a pretty simple parent/child relationship here, which looks like this:

Email servers have n folders.
Folders can have n (sub-)folders.
Folders have a reference to their parent folder as well as to the email server they belong to.

My mapping files look like this:

MailServer.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">
<!-- Generated 02.05.2011 12:32:52 by Hibernate Tools 3.3.0.GA -->
<hibernate-mapping>
    <class name="test.MailServer" table="MAILSERVER">

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

        <bag name="folders" table="FOLDERS" lazy="false" inverse="true" cascade="all-delete-orphan">
            <key column="MAIL_SERVER_ID"></key>
            <one-to-many class="test.Folder" />
        </bag>

    </class>
</hibernate-mapping>

Folder.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">
<!-- Generated 04.05.2011 15:02:31 by Hibernate Tools 3.3.0.GA -->
<hibernate-mapping>
    <class name="test.Folder" table="FOLDERS">

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

        <many-to-one name="mailServer" column="MAIL_SERVER_ID" not-null="true" />

        <bag name="folders" table="FOLDERS" lazy="false" inverse="true" cascade="all">
            <key column="PARENT_FOLDER_ID" not-null="false"></key>
            <one-to-many class="test.Folder" />
        </bag>

        <many-to-one name="parentFolder" column="PARENT_FOLDER_ID" />

    </class>
</hibernate-mapping>

The problem I got, is the following.

Let’s say, I have the following hierachy:

- MyMailServer
    Folder1
  - Folder2
      Subfolder
    Folder3

When I call hibernateSession.save(mailServerInstance); or hibernateSession.update(mailServerInstance);, Hibernate correctly stores everything to the database. The parent column id’s are filled correctly. Same for all other references.

BUT when I load the data, Hibernate reloads the folder hierachy like this:

- MyMailServer
    Folder1
    Folder2
    Subfolder
    Folder3

I understand the reason: Subfolder has a reference to its MailServer and thus, Hibernate ads it there instead of the folder where it belongs to.

But, how do I solve this problem?

Thanks in advance!

Answer 1

I worked around this by replacing

<bag name="folders" table="FOLDERS" lazy="false" inverse="true" cascade="all-delete-orphan">
    <key column="MAIL_SERVER_ID"></key>
    <one-to-many class="test.Folder" />
</bag>

in MailServer.hbm.xml with

<one-to-one name="rootFolder" class="test.Folder" cascade="all" />

That did the trick.