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Asked: 2026-05-26T14:14:16+00:00

There is a Java SE project with Hibernate ORM. I feel that the problem

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There is a Java SE project with Hibernate ORM. I feel that the problem is trivial, but need some help.

There is a code snippet:

    SessionFactory factory = new Configuration().configure().buildSessionFactory();

    Session s = factory.openSession();

    int id = 1;

    ExperimentSetResult experimentSetResult = (ExperimentSetResult)s.get(ExperimentSetResult.class, id);

    System.out.println("size: " + experimentSetResult.getExperimentResults().size());
    System.out.println("id[0]: " + experimentSetResult.getExperimentResults().get(0).getId());

I get a NullPointerException for the last string of code (when accessing the 0-th element of a collection associated with an object loaded recently).

There are the hbm files snippets:

ExperimentResult.hbm.xml:

<hibernate-mapping>
    <class name="rmocommon.driverreaction.ExperimentResult" table="experiment_results">
        <id name="id" type="int">
            <generator class="increment"/>
        </id>
        <many-to-one class="rmocommon.driverreaction.ExperimentSetResult" name="ExperimentSetResult" column="ExperimentSetResultId" not-null="true" />
    </class>
</hibernate-mapping>

ExperimentSetResult.hbm.xml:

<hibernate-mapping>
    <class name="rmocommon.driverreaction.ExperimentSetResult" table="experiment_set_results">
        <id name="id" type="int">
            <generator class="increment"/>
        </id>

        <list name="ExperimentResults" cascade="all-delete-orphan" inverse="true">
            <key column="ExperimentSetResultId" not-null="true"/>
            <list-index column="Id"/>
            <one-to-many class="rmocommon.driverreaction.ExperimentResult"/>
        </list>    
    </class>
</hibernate-mapping>

What’s wrong with mapping or with my source code?

UPDATE:
Here is an output and a stack trace:

Hibernate: select experiment0_.id as id4_2_, experiment0_.StartedDate as StartedD2_4_2_, experiment0_.FinishedDate as Finished3_4_2_, experiment0_.DeviceOutput as DeviceOu4_4_2_, person1_.id as id0_0_, person1_.Login as Login0_0_, person1_.LastName as LastName0_0_, person1_.Patronymic as Patronymic0_0_, person1_.FirstName as FirstName0_0_, person1_.Age as Age0_0_, experiment2_.id as id1_1_, experiment2_.TestMode as TestMode1_1_, experiment2_.TransportType as Transpor3_1_1_, experiment2_.TransportStartSpeed as Transpor4_1_1_, experiment2_.RoadType as RoadType1_1_, experiment2_.RoadLength as RoadLength1_1_, experiment2_.DirectionLeft as Directio7_1_1_, experiment2_.RespondToFirstEffort as RespondT8_1_1_, experiment2_.SoundOnFirstEffort as SoundOnF9_1_1_, experiment2_.ScaleObjects as ScaleOb10_1_1_, experiment2_.ShowTransportSpeed as ShowTra11_1_1_, experiment2_.BarrierXMin as Barrier12_1_1_, experiment2_.BarrierXMax as Barrier13_1_1_, experiment2_.ReactionTime as Reactio14_1_1_, experiment2_.SoundOnBarrierAppearance as SoundOn15_1_1_, experiment2_.AllowedCheatCount as Allowed16_1_1_ from experiment_set_results experiment0_ left outer join persons person1_ on experiment0_.id=person1_.id left outer join experiment_set_settings experiment2_ on experiment0_.id=experiment2_.id where experiment0_.id=?
Hibernate: select experiment0_.ExperimentSetResultId as Experim11_4_1_, experiment0_.id as id1_, experiment0_.Id as Id1_, experiment0_.id as id2_0_, experiment0_.Distance as Distance2_0_, experiment0_.Crash as Crash2_0_, experiment0_.BrakingStarted as BrakingS4_2_0_, experiment0_.BrakingStartedTime as BrakingS5_2_0_, experiment0_.BrakingStartedDistance as BrakingS6_2_0_, experiment0_.BarrierX as BarrierX2_0_, experiment0_.Number as Number2_0_, experiment0_.Time as Time2_0_, experiment0_.Valid as Valid2_0_, experiment0_.ExperimentSetResultId as Experim11_2_0_ from experiment_results experiment0_ where experiment0_.ExperimentSetResultId=?
size: 6
Exception in thread "main" java.lang.NullPointerException
    at hibernateTest.HibernateTest.main(HibernateTest.java:45)
Java Result: 1
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1 Answer

  1. Editorial Team

    Might be that your mapping is wrong. Your list-index column definetly should not be ID.
    If you really need the ordering, you better create a separate column for that, otherwise you will encounter problems.

    Another thing I’ve noticed. You don’t have to specify the inverse on the one-to-many relationship.

    It’s been a while I’ve seen hbm.xml files, can you use annotations? They are much easier to understand.

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