I have one usage scenario as below:
The classes could be like this.
public class Person {
...
List Addresses; //A list of Address objects.
}
public class Address {
...
List types; //A list of AddressType object
}
public class AddressType {
long typenum;
String typename;
}
The database schema could be like this.
creat table addressType (
typenum varchar(20) primary key,
typename varchar(40) not null
);
/*
* Table models a collection of address type.
*/
create table addressTypes (
collectionID integer,
type integer,
constraint FK_ADDRESSTYPE_TO_STRING foreign key
(type) references addresstype (typenum)
);
create sequence seq_ats;
create table person (
id integer primary key,
...
);
create table address (
personid integer not null,
...
types integer, /* The type references the
collectionID in the AddressTypes above */
constraint FK_ADDRESS_TO_PERSON foreign key
(companyid) references person (id)
);
The mapping file is like this
<hibernate-mapping>
<bag role="addressTypes" table="addressTypes">
<generated-key type="long" column="collectionID">
<generator class="sequence">
<param>seq_ats</param>
</generator>
</generated-key>
<composite-element class="AddressTypeWrapper">
<many-to-one name="type" column="type"
class="AddressType"/>
</composite-element>
<!--
here I use one component class AddressTypeWrapper to
wrap the AddressType object. The AddressTypeWrapper
has only one property: the AddressType object. So
here the AddressTypeWrapper is really an artifact
class required for hibernate mapping only, not from
object model.
What I really wants is that the collection element is
type of AddressType, not AddressTyepWrapper. The
mapping could be like this: <many-to-one name="type"
column="type"
class="AddressType"/>---<many-to-one>directly under
<bag>.
However this is not allowed by the DTD since bag does
not have <many-to-one> element.
Is there any other consideration why <many-to-one> is
not allowed here? or Can I just modify the DTD and use
the <many-to-one> directly under <bag>.
On a second though <many-to-one>/<one-to-one> should
be allowed anywhere <property>/<element> is allowed.
For <property>/<element>, One column produce an
instance of primitive type. For
<many-to-one>/<one-to-one> one column (and a table) is
used to produce a user-defined type.
-->
</bag>
<!-- map for AddressType -->
<class name="AddressType" table="AddressType">
<id name="typenum" type="long">
...
</id>
<property name="typename" column="typename"/>
</class>
<!-- map for Person -->
<class name="Person" table="person">
...
<!--person has a list of Address -->
<bag name="addresses table="address">
<key column="personid"/>
<composite-element>
...
<!-- references to the top-level collection -->
<collection name="types" column="types"
role="addressTypes"/>
</composite-element>
</bag>
</class>
</hibernate-mapping>
Thanks
jason
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