Hi
I am using hibernate 3 and Spring 2.
I have noticed when I save newly created parent object along with a list of child objects, (also newly created) with the id generator sequence (oracle)the foreign key field in the child objects are saved to the DB but not into the objects themselves:
I have class Publisher which has a collection of objects of type Author: set<Author> authors. the mapping file for Publisher:
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<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.test.domain">
<class name="Publisher" table="PUBLISHERS" schema="MYSCHEMA" lazy="false">
<id name="id" type="java.lang.Long">
<column name="PUBLISHER_ID" precision="22" scale="0" />
<generator class="sequence">
<param name="sequence">PUBLISHER_ID</param>
</generator>
</id>
<property name="name" type="java.lang.String">
<column name="NAME" length="100" not-null="true" />
</property>

</property>
<set name="authors" cascade="all" table="AUTHORS" lazy="false">
<key column="PUBLISHER_ID"/>
<one-to-many class="Author"/>
</set>
</class>
</hibernate-mapping>
*************************************************
mapping file for Author:
************************************************
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping package="com.test.domain">
<class name="Author" table="AUTHORS" schema="MYSCHEMA" lazy="false">

<id name="id" type="java.lang.Long">
<column name="AUTHOR_ID" precision="22" scale="0" />
<generator class="sequence">
<param name="sequence">AUTHOR_ID</param>
</generator>
</id>

<property name="publisherId" type="java.lang.Long">
<column name="PUBLISHER_ID" precision="22" scale="0" />
</property>

<property name="displayName" type="java.lang.String">
<column name="DISPLAY_NAME" length="200" not-null="true" />
</property>

<property name="email" type="java.lang.String">
<column name="EMAIL" />
</property>

</class>
</hibernate-mapping>
*********************************************************
Here is the java code:
*****************************************************
Author author = new Author();
Publisher publisher = new Publisher();

try {

author.setDisplayName("Test Name");
author.setEmail("Test Email");



Set authors = new HashSet();
authors.add(author);


publisher.setAuthors(authors);
publisher.setName("Test PublisherName");


getHibernateTemplate().save(publisher);
System.out.println("Author.PublisherId = "+author.getPublisherId()); // output:"Author.PublisherId = null"


} catch (Exception e) {
System.out.println("Exception: "+e.getMessage());
e.printStackTrace();
}

**************************************************

It seems like hibernate generates id (primary keys) but fails to insert foreign keys. It also throws error if in the DB the foreign key (Author.publisherId) is set to NOT NULL, because as HQL shows, hibernate first creates two records (Publisher and Author) with two insert statements
and then updates author's publisherId.

Please tell me where I went wrong.
Many thanks.

I think you probably want to implement a bidirectional association there. There may be a circumstance that you would want to navigate the domain graph from Author to Publisher. Instead of this in your Author mapping:

Do this:


In the Publisher mapping, add inverse="true" to the set of Authors.

You will, of course, have to change your mapping files, changing the Author POJO from Long publisherId to Publisher publisher.

Also, you should add bidirectional association management routines in your POJO, as such (Publisher):


I leave it up to you to define an equivalent removeAuthor method.

More information on bi-directional associations here.

Does it mean that to make hibernate work correctly I have to make the relationship bidirectional and all unidirectional associations are doomed to work wrong?