one-to-many list mapping

[Ionut Barau]

Hi! I have difficulty understanding one to many mapping with lists. I use Oracle 10g and Hibernate 3. I have class Artist and class Song. Artist has a List of Song objects as field and Song has a Artist field. As far as I know I have to make a many-to-one association in Song.hbm.xml and a one-to-many association in Artist.hmb.xml. Now Song table has a foreign key to Artist table but Artist table doesn't have a foreing key to Song. I want to be able to load the Artist previously persited(I've also persisted Song objects) and iterate thru the Artist's list of Song objects. When i try this I get org.hibernate.HibernateException: null index column for collection which is obviously because I don't have a column Songs. My question is it is possible to do this (and if it is what have I done wrong in the mapping files) or do I have a problem understanding db design?If it isn't possible I think mapping collections isn't worth.

Here is the one-to many association of Artist.hmb.xml

 
 <list name="songs" inverse="true" table="SONG" lazy="true" >
        
            <key>
                <column name="ARTIST" />
            </key>
            <index/>
            <one-to-many class="domain.Song" />
        </list>

   

And here is the many to one association of Song.hmb.xml:

  
 <many-to-one name="artist" class="domain.Artist" fetch="join" >
            <column name="ARTIST" not-null="true"/>
        </many-to-one>
  

[Karthik Shiraly]

Hi,

list collection in mapping is used if the order of items is important and you have a column that stores the index number of the item.
It doesn't seem to be the case in your example. If you don't need the ordering, use a set collection and change your class to use a java.util.Set.

[Ionut Barau]

The subject of the topic was not good. It don't understand collection mapping, it doesn't matter the type. I want to be able when i load an Artist to get his Songs with his getSongs() method. But i get a org.hibernate.HibernateException: null index column for collection error.