Hi,

I am new to Hibernate, and have hit on the following problem :

I have a class has a composite element of a HashMap, which contains key-value pairs of : String - MyInterface.

Different instances of the class may have different implementations of MyInterface as the value in the Map.

The error traces below occur when I try to retrieve the instance (it persists without any problem), as I assume Hibernate is trying to instantiate the Interface.

Other than creating seperate identical classes and seperate mapping files, can anyone suggest how best to implement this?

Any advice would be greatly appreciated ...



Hibernate version:3.0.5

Mapping documents:
<hibernate-mapping package="somebusiness">

<class name="SomeInstance" table="gen_inst">
<id name="id" column="uid" type="long">
<generator class="identity"/>
</id>
<property name="instanceName" type="string" />
<map name="configObjects" table="portlet_instance" cascade="all">
<key column="map_instance_id"/>
<index column="some_name" type="string"/>
<many-to-many column="config_bean" class="MyInterface"/>
</map>
</class>

<class name="MyInterface" table="the_interface">
<id name="id" column="uid" type="long">
<generator class="identity"/>
</id>
<property name="someAttribute" type="string" length="20"/>
</class>

</hibernate-mapping>




Full stack trace of any exception that occurs:
INFO: Error performing load command
org.hibernate.InstantiationException: Cannot instantiate abstract class or interface: somebusiness.MyInterface
at org.hibernate.tuple.PojoInstantiator.instantiate(PojoInstantiator.java:56)


Name and version of the database you are using: IBM UDB 7

Your mapping file needs to tell Hibernate which are the concrete classes to instanciate. Take a look at inheritance mapping :

http://www.hibernate.org/hib_docs/v3/reference/en/html/inheritance.html