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Hi everybody,

I am new to Hibernate and as a matter of fact I am using it for my dissertation project. I have already successfully implemented: associations (bidirectional and many-to-many) and inheritance but I am not that clear on one-to-many composition mapping. My application is the cd store and part of it is composition between the CD class and the Track class since a CD has many tracks. The CD class defines:


and the Track class defines:



Furthermore part of the database schema defines the cd and track tables in a one-to-many relationship where the cdID is a foreign key column in the track table.

In my first cut design there was no CD object field in the Track class and Hibernate was throwing exceptions left and right. Once I included the object field everything goes smoothly and the client displays the CD details and lists the tracks.
My question is probably naïve but I really want to know whether I mapped composition or a one-to-many association? My intention is to map one-to-many composition so did I implement it correctly?

Many thanks,
Nick.


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>

<!-- Inheritance mapping strategy: One table per class hierarchy -->
<class name="cdstore.CD" table="cd">

<!-- Parent class mapping -->
<id name="id" type="integer" column="cdID">
<generator class="native"/>
</id>

<!-- Value identifying the type of the child class -->
<discriminator column="format" type="string"/>

<property name="cdTitle" type="string"
column="title" not-null="true"/>
<property name="releaseDate" type="string"
column="released" not-null="true"/>
<property name="label" type="string"
column="label" not-null="true"/>

<!-- Map association to relationship -->
<many-to-one name="act" class="cdstore.Act" column="actID" not-null="true"/>

<!-- Composition mapping to 1:M relationship -->
<set name="tracks" table="track" inverse="true">
<key column="cdID"/>
<one-to-many class="cdstore.Track"/>
</set>

<!-- Subclass mapping -->
<subclass name="cdstore.CDsingle" discriminator-value="Single">
<property name="price" column="price"/>
</subclass>
<subclass name="cdstore.CDalbum" discriminator-value="Album">
<property name="price" column="price"/>
</subclass>
<subclass name="cdstore.DoubleCD" discriminator-value="Double">
<property name="price" column="price"/>
</subclass>

</class>

</hibernate-mapping>


<?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>

<!-- -->
<class name="cdstore.Track" table="track">

<!-- -->
<id name="id" type="integer" column="trackNo">
<generator class="native"/>
</id>

<property name="trackTitle" type="string"
column="trackName" not-null="true"/>

<!-- -->
<many-to-one name="cd" class="cdstore.CD" column="cdID"/>

</class>

</hibernate-mapping>



Code between sessionFactory.openSession() and session.close():

Full stack trace of any exception that occurs:

Name and version of the database you are using: MySQL 4.1.14

The generated SQL (show_sql=true):

Debug level Hibernate log excerpt:

Hi,
I dont think you have to define an object of CD in the Track Class. Can you post the exception that is being thrown when you dont define the same.

Tables : A > B

Want to have One - Many from A > B

Define One-Many Mapping in A.xml , and the corresponding Set Definition in the Value Object.

Similarly Many to One from B > A
Define Many-to-One in B.xml and the corresponding Object Definiton in Value Object.

You need not necessarly have both at the same time

Cheers
Vijay