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Subclassing without discriminators (rather joins)

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young_matthewd

Post subject: Subclassing without discriminators (rather joins)

Posted: Wed Feb 01, 2006 6:17 am

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Joined: Sun Oct 09, 2005 3:21 pm
Posts: 40

Hibernate version: 3.1.1

Mapping documents:

Code:

<class name="Resurs" table="RESURS">

   <id name="id">
      <column name="RESURSID" sql-type="INTEGER"/>
      <generator class="identity">
      </generator>
   </id>

   ....(more)

                <set name="resurs1Relationer" lazy="true" inverse="true" cascade="save-update" where="TOMTSTAMP is null">
      <key column="RESURSID1" on-delete="noaction" not-null="true"/>
      <one-to-many class="ResursRelation"/>
   </set>

                ....(more)
</class>

<class name="ResursRelation" table="RESURSRELATION">

   <id name="id">
      <column name="RESRELID" sql-type="INTEGER"/>
      <generator class="identity">
      </generator>
   </id>

   <many-to-one lazy="false" name="resurs1" class="Resurs" foreign-key="FK_RESREL_RES1" index="RESURSRELATION_FK">
      <column name="RESURSID1" sql-type="INTEGER"/>
         </many-to-one>

   <many-to-one lazy="false" name="resurs2" class="Resurs" foreign-key="FK_RESREL_RES2" index="RESURSRELATION_FK">
      <column name="RESURSID2" sql-type="INTEGER"/>
   </many-to-one>

   <many-to-one lazy="false" name="typ" class="ResursRelationtyp" foreign-key="FK_RESRELT_RESREL" index="RESURSRELATION_FK">
      <column name="RESRELTYPID" sql-type="INTEGER"/>
   </many-to-one>

                ......(more)

</class>

<class name="ResursRelationtyp" table="RESURSRELATIONTYP">

   <cache usage="read-only"/>

   <id name="id">
      <column name="RESRELTYPID" sql-type="INTEGER"/>
      <generator class="identity">
      </generator>
   </id>

   <property name="beteckning">
      <column name="BETECKNING" length="50" not-null="true"/>
   </property>

                .....(more)

</class>

Name and version of the database you are using: DB2 V8.2

[b]Problem: [b]
Want to subclass the ResursRelation based on the RESRELTYPID column without using a discriminator relying on a subselect to the ResursRelationtyp class (associated through the RESRELTYPID column). Would like to use a join somehow rather than a pure discriminator since with DB2 does not allow subselects a conditions of inner joins (ie. will happen when I start searching after Resurs objects connected to ResursRelation - see set definition - and want a particular subclass of the ResursRelation class based on ResursRelationtyp). Is there any inheritance model usable via Hiberante? Ideas?

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young_matthewd

Post subject: Simplifying my question

Posted: Wed Feb 01, 2006 5:24 pm

Beginner

Joined: Sun Oct 09, 2005 3:21 pm
Posts: 40

Maybe I should lighten my original question. Say you have two tables:
1) a table holding resource objects (discernable by type)
2) another table containing all of the resource types

One way to subclass the resource table is by using a discriminator that ties the foreign key relationship to a string value that each subclass may use (i.e. textual replacement for the natural index - numeric sequence generated by a database that isn't too transferrable between database instances making a name column more reasonable).

What I am looking for is a way to subclass via a join of the two tables (with a where clause on the name of the type of resource) but still mapping my subclass to the resource table.

Any ideas?

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young_matthewd

Post subject: Maybe subselect (ie.view) with sql-insert/sql-update

Posted: Wed Feb 15, 2006 6:06 pm

Beginner

Joined: Sun Oct 09, 2005 3:21 pm
Posts: 40

Still wondering if my original problem can be solved...

What if I made a class similar to ResursRelation:

Code:

<class name="ResRelSubQuery" mutable="false">
  <subselect>
    select t1.c1,t1.c2,t1.c3 .....
    from resursrelation t1, resurs t2, resurstyp t3
    where t1.resursid1=t2.resursid
    and t1.tomtstamp is null
    and t2.resurstypid=t3.resurstypid
    and t3.beteckning='version'
  </subselect>
  <id name="c1"/>
  <property name="c2" ..../>
   ....

  <sql-insert>
     insert into resursrelation (c2,c3,...) values (?,?,...)
  </sql-insert>
  ....
</class>

So that the ResRelSubQuery is really a view of the ResursRelation table (ie. immutable) but inserts/updates may occur via the sql-insert/sql-update tags. Is something like this possible. Or will the subselect force the class to be truely read-only (ie. no inserts/updates allowed).

If I had a ResRelSubQuery class like the above then I could map a set from the Resurs subclasses to permutations of the ResRelSubQuery class and solve the original problem.

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