Polymorphism mapping issues (bug?)

bonnyr · **Posted:** Tue Mar 01, 2005 11:36 pm

Hibernate version: 3.0b4

Following is an excerpt of a mapping document which has the problem
Mapping documents:

Code:

    <class name="NetworkObject" abstract="true">
        <id name="id"
            type="int"
            column="ID"
            unsaved-value="-1">
            <generator class="native"/>
        </id>

        <discriminator column="OBJ_TYPE" type="string"/>

        <version name="version"
                 type="int"
                 column="VERSION"/>

        <!-- Common name property. -->
        <property name="name"
                  type="string"
                  column="NAME"
                  length="100"
                  update="false"/>

     < ... other properties ommited ... >


        <!--
            define base hierarchy classes.

            Note the referenced classes are synthetic classes only used to support
            the Hibernate inheritance mechanism which only allows union-subclass to
            exist as a child element of class and cannot exist as a child of hibernate-mapping.

            Each concrete hierarchy root defines a private version of the 'Base' class to satisfy Hibernate
        -->
        <union-subclass name="BaseNE" abstract="true" table="NE" />
        <union-subclass name="BasePort" abstract="true" table="PORT"/>
table="ROUTE"/>-->

    <subclass name="NE" extends="BaseNE">
    <....>
    </subclass>

    <!-- Port Hierarchy (mapped into its own table, specified in BasePort -->
    <subclass name="Port" extends="BasePort">
        <property name="slot" type="int" column="SHELF_SLOT"/>
        <property name="index" type="int" column="PORT_INDEX"/>
       
        <many-to-one name="ne"
            class="NE"
            column="NE_ID" />

         < ... >
    </subclass>

    <subclass name="ATMPort" extends="Port" discriminator-value="A"/>
    <subclass name="GEPort" extends="Port" discriminator-value="G"/>

The intention is to have all classes derived from NetworkObject reside in
several tables, one per sub-hierarchy, whilst still having all the properties
defined in NetworkObject above. Secondly there's a couple of other classes, not mentioned here, which have references to NetworkObject type objects (collections thereof).

This mapping code is compiled/parsed successfully by the SchemaExport
tool and generates a ddl fragment. The problem stems from the fact
that the generated tables do not have a primary key constraint generated
for them and so, generated foreign keys like the NE_ID in the Port subclass above cannot be created since the NE table does not have the ID column (as inherited
from NetworkObject) as primary key.

Can I use this technique at all to achieve what I want?

Looking at the code, Port and NE are both instances of DenormalizedTable
and it seems that it does not use the idValue property of the included
table. Is this a bug?