"Incompatible data types in combination" leading to "Could not initialize a collection" in JPA with an inherited bidirectional relation

Question

I am trying to implement the following diagram in Hibernate, JPA.

I tried to implement it this way.

For the farm

@Entity
public class Farm implements Serializable{

    @OneToMany(mappedBy = "farm", cascade = { CascadeType.ALL }, targetEntity=AbstractAnimals.class, fetch=FetchType.LAZY)
    private List<AbstractAnimal> animals = new ArrayList<AbstractAnimals>();

}

For the Abstract Annimal

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class AbstractAnimal implements Serializable{
    @Id
    private int id;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "farmId", nullable = false)
    private Farm farm;

    ... other attributes and getter and setter
}

For the Abstract Mammalian

@MappedSuperClass
public abstract class AbstractMammalian extends AbstractAnimal implements Serializable{
    ... other attributes and getter and setter
}

For all the annimals

@Entity
public abstract class 'Animal' extends 'supertype' implements Serializable{

    ... other attributes and getter and setter
}

When I tried to get all the farm animals I get the following error

org.hibernate.exception.SQLGrammarException: could not initialize a collection: [my.example.Farm.animals#24]
    at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:92)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
    at org.hibernate.loader.Loader.loadCollection(Loader.java:2173)
    at org.hibernate.loader.collection.CollectionLoader.initialize(CollectionLoader.java:62)
    at org.hibernate.persister.collection.AbstractCollectionPersister.initialize(AbstractCollectionPersister.java:627)
    at org.hibernate.event.def.DefaultInitializeCollectionEventListener.onInitializeCollection(DefaultInitializeCollectionEventListener.java:83)
    at org.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:1863)
    at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:369)
    at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:111)
    at org.hibernate.collection.PersistentBag.iterator(PersistentBag.java:272)
    at my.example.persistence.Farm.getAnnimals(Farm.java:132)
    at my.example.DTOFactory.updateFarmDTO(DTOFactory.java:269)
    at my.example.DTOFactory.createFarmDTO(DTOFactory.java:250)
    at my.example.DTOFactory.createChickenDTO(DTOFactory.java:183)
    at my.example.ChickenServiceImpl.createChicken(ChickenServiceImpl.java:62)
    at my.example.ChickenServiceTest.createChickenWithHome(ChickenServiceTest.java:243)
    at my.example.ChickenServiceTest.testRejectChickenHome(ChickenServiceTest.java:186)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
    at org.junit.runners.BlockJUnit4ClassRunner.runNotIgnored(BlockJUnit4ClassRunner.java:79)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:71)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: java.sql.SQLSyntaxErrorException: incompatible data types in combination
    at org.hsqldb.jdbc.Util.sqlException(Unknown Source)
    at org.hsqldb.jdbc.Util.sqlException(Unknown Source)
    at org.hsqldb.jdbc.JDBCPreparedStatement.<init>(Unknown Source)
    at org.hsqldb.jdbc.JDBCConnection.prepareStatement(Unknown Source)
    at org.hibernate.jdbc.AbstractBatcher.getPreparedStatement(AbstractBatcher.java:534)
    at org.hibernate.jdbc.AbstractBatcher.getPreparedStatement(AbstractBatcher.java:452)
    at org.hibernate.jdbc.AbstractBatcher.prepareQueryStatement(AbstractBatcher.java:161)
    at org.hibernate.loader.Loader.prepareQueryStatement(Loader.java:1700)
    at org.hibernate.loader.Loader.doQuery(Loader.java:801)
    at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
    at org.hibernate.loader.Loader.loadCollection(Loader.java:2166)
    ... 40 more
Caused by: org.hsqldb.HsqlException: incompatible data types in combination
    at org.hsqldb.error.Error.error(Unknown Source)
    at org.hsqldb.error.Error.error(Unknown Source)
    at org.hsqldb.types.BitType.getAggregateType(Unknown Source)
    at org.hsqldb.types.Type.getAggregateType(Unknown Source)
    at org.hsqldb.QuerySpecification.resolveTypesPartOne(Unknown Source)
    at org.hsqldb.QueryExpression.resolveTypesPartOne(Unknown Source)
    at org.hsqldb.QueryExpression.resolveTypes(Unknown Source)
    at org.hsqldb.ParserDQL.XreadTableSubqueryOrNull(Unknown Source)
    at org.hsqldb.ParserDQL.readTableOrSubquery(Unknown Source)
    at org.hsqldb.ParserDQL.XreadTableReference(Unknown Source)
    at org.hsqldb.ParserDQL.XreadFromClause(Unknown Source)
    at org.hsqldb.ParserDQL.XreadTableExpression(Unknown Source)
    at org.hsqldb.ParserDQL.XreadQuerySpecification(Unknown Source)
    at org.hsqldb.ParserDQL.XreadSimpleTable(Unknown Source)
    at org.hsqldb.ParserDQL.XreadQueryPrimary(Unknown Source)
    at org.hsqldb.ParserDQL.XreadQueryTerm(Unknown Source)
    at org.hsqldb.ParserDQL.XreadQueryExpressionBody(Unknown Source)
    at org.hsqldb.ParserDQL.XreadQueryExpression(Unknown Source)
    at org.hsqldb.ParserDQL.compileCursorSpecification(Unknown Source)
    at org.hsqldb.ParserCommand.compilePart(Unknown Source)
    at org.hsqldb.ParserCommand.compileStatement(Unknown Source)
    at org.hsqldb.Session.compileStatement(Unknown Source)
    at org.hsqldb.StatementManager.compile(Unknown Source)
    at org.hsqldb.Session.execute(Unknown Source)
    ... 49 more

Edit

EntityManager manager = null;
EntityTransaction tx = null;
TaskDTO result = null;

try {
    manager = PersistenceUtils.getEntityManager();
    try
    {
       tx = manager.getTransaction();
       tx.begin();
       Farm farm = manager.find(Farm.class, 
       Farmer farmer = manager.find(farmer.class, farmerDtoID);
       int status = AnimalService.IDLE;

       if (birth.before(new Date())){
           status = TaskService.UNBORN;
       }
       Chicken newChicken = new Chicken(name, farm, user, birth, death, status);
       manager.persist(newChicken);
       tx.commit();
       result = DTOFactory.createChickenDTO(newChicken, true);
   }
   finally
   {
       if (tx.isActive())
       {
           tx.rollback();
       }
   }
}
finally
{
    if (manager != null)
    {
        manager.close();
    }
 }
 return result;

Answer 1

I have no idea what you're doing wrong. You just haven't shown us enough code to detect the problem.

Here is how you can do it right:

• https://bitbucket.org/twic/farm/src

That is an implementation of the same object model, but in a way which works fine. There is a Gradle script which will generate and apply the relevant SQL; you can then run the Main class to insert and query some data, including calling Farm.getAnimals().

There are a few differences between my code and yours. Mine is simpler; i have left out the various unnecessary things like specifying column names, explicitly stating that collections are lazy, making entity classes serializable, etc. I have also opted to annotate AbstractMammal as an @Entity, not a @MappedSuperclass. I saw no reason not to. I tried it both ways, and both ways worked.

So, whatever it is that's going wrong for you, it is a difference between your code and mine. It could be a bug in your JPA implementation. It is more likely to be a bug in your annotations. I suggest you clone my code, make it run, then start modifying it bit by bit to be more like your code, and see when it breaks.