Advice for daealing with inheritance correctly

tradem · **Joined:** Mon Oct 06, 2003 1:59 am **Posts:** 52

Hi Folks,

which kind of inheritance is the best way to map the
Accountability Analyis Pattern?

Here we have:

As you can see Person and Organiation are both Parties. This it correct to map the using <many-to-any> and many-to-one in (abstract) Party class.

Here what I did:

Code:

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
    <class
        name="de.grob.portal.domain.model.Accountablity"
        table="ACCOUNTABILITIES"
        proxy="de.grob.portal.domain.model.Accountablity"
        dynamic-update="false"
        dynamic-insert="false"
    >

        <id
            name="accountId"
            column="ACCOUNT_ID"
            type="long"
        >
            <generator class="native">
            </generator>
        </id>

        <set
            name="timePeriods"
            lazy="true"
            inverse="false"
            cascade="none"
            sort="unsorted"
        >

              <key
                  column="TIME_PERIOD_ID"
              />

              <one-to-many
                  class="de.grob.portal.domain.model.TimePeriod"
              />
        </set>

        <set
            name="types"
            lazy="false"
            inverse="false"
            cascade="none"
            sort="unsorted"
        >

              <key
                  column="ACCOUNT_TYPE_ID"
              />

              <one-to-many
                  class="de.grob.portal.domain.model.AccountablityType"
              />
        </set>

       <set name="comissioners" lazy="true" inverse="false" cascade="none" sort="unsorted">
      <key column="COMISSIONER_ID"/>
      <many-to-any
        id-type="string">
        <!-- Person, Organization, Post -->         
        <column name="COMISSIONER_TYPE"/> 
        <column name="COMISSIONER_ID"/>          
      </many-to-any>
   </set>
   <set name="responsibles" lazy="true" inverse="false" cascade="none" sort="unsorted">
      <key column="RESPONSIBILITY_ID"/> 
      <many-to-any        
        id-type="string">
        <!-- Person, Organization, Post -->    
        <column name="RESPONSIBILITY_TYPE"/>    
        <column name="RESPONSIBILITY_ID"/>          
      </many-to-any>
   </set>

    </class>

</hibernate-mapping>

<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN" 
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
    <class
        name="de.grob.portal.domain.model.Person"
        table="PERSONS"
        proxy="de.grob.portal.domain.model.Person"
        dynamic-update="false"
        dynamic-insert="false"
    >

        <id
            name="personId"
            column="PERSON_ID"
            type="long"
        >
            <generator class="native">
            </generator>
        </id>

    
        <many-to-one
            name="comissioner"
            class="de.grob.portal.domain.model.Accountablity"
            cascade="none"
            outer-join="auto"
            update="true"
            insert="true"
            column="ACCOUNT_COMMISSIONER_FK"
        />

     

        <one-to-one
            name="responsbile"
            class="de.grob.portal.domain.model.Accountablity"
            cascade="none"
            outer-join="auto"
            constrained="true"
        />

    

    </class>   

</hibernate-mapping>

Or is it petter to use a different kind of mapping. As you can see Parties should be interchanable in Accountablity class.

Is there a common rule when to choose one of the thre inheritance mapping strategies?

Thx a lot!!!!

Bye
Toby

emmanuel · **Posted:** Mon May 03, 2004 7:30 pm

Why not using subclass (type as discriminator) instead of the bad and slow *-to-any

tradem · **Joined:** Mon Oct 06, 2003 1:59 am **Posts:** 52

emmanuel wrote:

Why not using subclass (type as discriminator) instead of the bad and slow *-to-any

I already meditated about this solution. But this breaks the rational mantra IMHO, if not please let me know.

As you can image a Person as different attributes as a Organization or a Post. As all of this types are Parties the table per hierachy will end up in a suop of entities. Did I misread the docs? Using a discriminator and subclass may force me to use a single soup table, right?

Any chance to use joined-subclass ?

Why is *-to-any so bad? Could you please provide more technial details ;) ?

emmanuel · **Posted:** Wed May 05, 2004 12:30 pm

*-to-any break every single mantra hinduists have ever think of ;-)

what do you mean by a "soup of entities"? Yes you table will keep the whole hierarchy and you'll face null values in your rows.
You can check joined-subclass for mapping a hierarchy having lots of different properties in subclasses.

*-to_any will need an extra query to load the any object, it's hard to use by third party applications and it breaks the relational model.

tradem · **Joined:** Mon Oct 06, 2003 1:59 am **Posts:** 52

emmanuel wrote:

*-to-any break every single mantra hinduists have ever think of ;-)

what do you mean by a "soup of entities"? Yes you table will keep the whole hierarchy and you'll face null values in your rows.
You can check joined-subclass for mapping a hierarchy having lots of different properties in subclasses.

Okay. It try it know with joined-subclasses. With soup I mean "keep the whole hierarchy" in one table. From OO perspectivce this is not so clean ;) I mean there is some sort of gap between mapped objectes and database entities....

As far as I can see hibernate provides a good solution with joinded-subclasses.

So as far as I understand the docs the abstract class can be used as normaly one-to-many mapping within every kind of collection and therefore threaten transparently like every other mapped domain model pojo, right?

Thx
Toby

emmanuel · **Posted:** Thu May 06, 2004 11:19 am

For a relational perspective, what you call a entity soup is perfectly valid