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How to map class including <set> of abstract classes?

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lukashh

Post subject: How to map class including <set> of abstract classes?

Posted: Thu Mar 02, 2006 2:01 pm

Newbie

Joined: Fri Jan 20, 2006 1:32 pm
Posts: 11

Hello,
I have a class Garage and I want it to have a <set> of Vehicles (abstract class). Concrete vehicles are "Car extends Vehicle" and "Truck extends Vehicle".

Following mapping doesn't work:

Code:

Caused by: java.sql.BatchUpdateException: Table 'database.Vehicle' doesn't exist

Garage

Code:

   <class name="Garage" table="garage">
      <id name="garageId" type="integer" column="garage_id">
         <generator class="increment" />
      </id>

      <property ...>

      <set name="vehicles">
         <key column="garage_id"></key>
         <one-to-many
            class="Vehicle" />
      </set>

   </class>

abstract Vehicle

Code:

   <class name="Vehicle" abstract="true">

      <id name="id" type="integer" column="id">
         <generator class="increment" />
      </id>
      
      <property ...>

      <union-subclass name="Car"
         table="car">
      </union-subclass>

      <union-subclass name="Truck"
         table="truck">
      </union-subclass>

   </class>

Thank you
Lucas

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lukashh

Post subject: Re: How to map class including <set> of abstract class

Posted: Thu Mar 02, 2006 4:01 pm

Newbie

Joined: Fri Jan 20, 2006 1:32 pm
Posts: 11

Well, I've put this (inverse, cascade) into mapping and it's ok

Code:

      <set name="vehicles" inverse="true" cascade="all">
         <key column="garage_id"></key>
         <one-to-many
            class="Vehicle" />
      </set>

But now I have always garage_id NULL, even when inverse="true" so set of vehicles dedicated to garage is always empty.

Any ideas?

Thank you

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alexism

Post subject: Re: How to map class including <set> of abstract class

Posted: Thu Mar 02, 2006 4:05 pm

Beginner

Joined: Thu Feb 16, 2006 9:53 am
Posts: 24

inverse attribute is usefull for bidirectional association.
Is there a "garage" attribute in Vehicle.java?

Could you provide the full mapping files and the code used to create objects, please?

Alexis

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lukashh

Post subject:

Posted: Thu Mar 02, 2006 4:37 pm

Newbie

Joined: Fri Jan 20, 2006 1:32 pm
Posts: 11

Garage

Code:

   <class name="Garage" table="garage">
      <id name="garageId" type="integer" column="garage_id">
         <generator class="increment" />
      </id>
      <property name="name" />

      <set name="vehicles" inverse="true" cascade="all">
         <key column="garage_id"></key>
         <one-to-many
            class="Vehicle" />
      </set>

   </class>

Vehicle

Code:

   <class name="Vehicle" abstract="true">

      <id name="id" type="integer" column="id">
         <generator class="increment" />
      </id>
      
      <property name="name" type="string" />

      <union-subclass name="Car"
         table="car">
      </union-subclass>

      <union-subclass name="Truck"
         table="truck">
      </union-subclass>
   </class>

Garage.java

Code:

public class Garage implements Serializable {
   
    private Set<Vehicle> vehicles;
.
.

Vehicle.java

Code:

public abstract class Vehicle implements Serializable {
    
    private Integer garage_id;
    .
    .

Creating objects

Code:

            tx = session.beginTransaction();

            Garage garage = new Garage("name");
 
            Vehicle vehicle = new Car("name");
            
            //session.save(vehicle);
            
            Set<Vehicle> set = new HashSet<Vehicle>();
            c.add(vehicle);
            garage.setVehicles(set);
            
            session.save(garage);
            tx.commit();

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alexism

Post subject:

Posted: Thu Mar 02, 2006 5:15 pm

Beginner

Joined: Thu Feb 16, 2006 9:53 am
Posts: 24

If your association is bidirectional (which seems to be your intention), you should declare a Garage type attribute (instead of an integer) and map it in Vehicle.hbm.xml.
(oversight?)

Something like:

Code:

<many-to-one name="garage"
                     class="Garage"
                     column="GARAGE_ID"/>

Moreover your Set is initialisation is quite ugly.
Just write :

Code:

private Set<Vehicle> vehicles = new HashSet();

If you actually choose to set the inverse & cascade attributes on the Garage side, you should add a "addVehicle(...)" method which would link the vehicle to the the garage:

Code:

public void addVehicle(Vehicle v){
     vehicles.add(v);
     v.setGarage(this);
}

So your main method becomes:

Code:

tx = session.beginTransaction();
Garage garage = new Garage("name");
Vehicle vehicle = new Car("name");
garage.addVehicle(vehicle);
session.save(garage);
tx.commit();

To conclude, may I advise you to read the following sections of the Reference Manual:
1.3.5. Bi-directional associations
1.3.6. Working bi-directional links

of course the reading of the full manual may be usefull ;)

Alexis
Don't forget to rate ;)

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lukashh

Post subject:

Posted: Fri Mar 03, 2006 8:54 am

Newbie

Joined: Fri Jan 20, 2006 1:32 pm
Posts: 11

Well, I solved it:

Hibernate manual says:

table per concrete-class (union-subclass)

Code:

<one-to-many> (for inverse="true" only)

So I cannot make unidirectional <one-to-many> using union-subclass aproach.
(but thank you for hints)

Lukas

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