DSClientFactory: AbstractClass Inheritance - Error while creating an instance of class

[Angoth]

Hi,
I'm currently evaluating Kundera with Datastax Cassandra and ran into some trouble reading my saved object. When I call entityManager.find, I get an ERROR c.i.k.u.KunderaCoreUtils - Error while creating an instance of class exception. The problem is, Kundera calls the Abstract Class constructor via reflections instead of the subclasses' contructors.

I've attached a simple example project with the problem.

Setup:
Datastax Enterprise Version 5.0.3
Cassandra 3.0
Kundera: 3.13
Driver: com.impetus.kundera.client.cassandra.dsdriver.DSClientFactory

Relevant classes:

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "computer_type", discriminatorType = DiscriminatorType.STRING)
public abstract class AbstractComputer extends AbstractEntity {

	@ManyToOne
	private Rack rack;

	@Column
	private double price;

	public Rack getRack() {
		return rack;
	}

	public void setRack(Rack rack) {
		this.rack = rack;
	}

	public double getPrice() {
		return price;
	}

	public void setPrice(double price) {
		this.price = price;
	}

}

@Entity
public class Rack extends AbstractEntity {

	@OneToMany(cascade = { CascadeType.ALL }, mappedBy = "rack")
	@JoinColumn(name = "rack")
	private List<AbstractComputer> computers;

	public List<AbstractComputer> getComputers() {
		return computers;
	}

	public void setComputers(List<AbstractComputer> computers) {
		this.computers = computers;
	}
}

@Entity
@DiscriminatorValue(value = "ComputerA")
public class ComputerA extends AbstractComputer {

	@Column
	private Date date;

	@Column
	private String manufacturer;

	public Date getDate() {
		return date;
	}

	public void setDate(Date date) {
		this.date = date;
	}

	public String getManufacturer() {
		return manufacturer;
	}

	public void setManufacturer(String manufacturer) {
		this.manufacturer = manufacturer;
	}
}

@Entity
@DiscriminatorValue(value = "ComputerB")
public class ComputerB extends AbstractComputer {

	@Column
	private BigDecimal tact;

	@Column
	private int cores;

	public BigDecimal getTact() {
		return tact;
	}

	public void setTact(BigDecimal tact) {
		this.tact = tact;
	}

	public int getCores() {
		return cores;
	}

	public void setCores(int cores) {
		this.cores = cores;
	}
}

TestCase:

@Test
public void testDB() {
	EntityManagerFactory factory = Persistence.createEntityManagerFactory(PERSISTENCE_UNIT_NAME);
	EntityManager em = factory.createEntityManager();

	Rack rack = new Rack();
	List<AbstractComputer> computers = new ArrayList<>();

	ComputerA computerA = new ComputerA();
	computerA.setDate(new Date());
	computerA.setManufacturer("HP");

	ComputerB computerB = new ComputerB();
	computerB.setCores(4);
	computerB.setTact(new BigDecimal("4.99"));

	computers.add(computerA);
	computers.add(computerB);
	rack.setComputers(computers);

	em.persist(rack);
	em.flush();
	em.clear();

	Rack loadedRack = em.find(Rack.class, rack.getId());
	loadedRack.getComputers(); // error

	em.close();
	factory.close();
}

KunderaIssue.zip

[devender-yadav]

Hi @Angoth, I will try to replicate this at my end.

[Angoth]

Hi @devender-yadav,
thanks for looking into the problem. Any news about the issue?

[devender-yadav]

Hi @Angoth, I got busy with other tasks. I will get back to you on this by tomorrow. Meanwhile can you please check these entites and testcase related to Inheritance - https://github.com/Impetus/Kundera/tree/c645d7f7e949a0e9f9b06b010e527725a4b0a3d2/src/kundera-cassandra/cassandra-core/src/test/java/com/impetus/kundera/client/crud/inheritence

[Angoth]

Thanks for your fast response.
I already checked these testcases and had the same problem with DsClient. ThriftClient was working though.

But in my next evaluation step I had some really nasty performance problems and timeout exceptions while persisting a rather complex data model and large datasets on a 4 nodes cluster. Interestingly the performance problems did't occur with DsClient.

But the performance problems are another topic... Would be nice to find a solution to the DsClient issue and I'll be awaiting your answer on the issue

[Angoth]

I did some debugging and perhaps here is some helpful information for you...

DsClient doesn't seem to have any check for SubTypes. In my opinion it should be in this method:

    private List iterateAndReturn(ResultSet rSet, EntityMetadata metadata) {
        MetamodelImpl metaModel =
            (MetamodelImpl) kunderaMetadata.getApplicationMetadata().getMetamodel(metadata.getPersistenceUnit());
        EntityType entityType = metaModel.entity(metadata.getEntityClazz());

        Iterator<Row> rowIter = rSet.iterator();
        List results = new ArrayList();

        Map<String, Object> relationalValues = new HashMap<String, Object>();

        while (rowIter.hasNext()) {
            Object entity = null;
            Row row = rowIter.next();
            populateObjectFromRow(metadata, metaModel, entityType, results, relationalValues, entity, row);
        }
        return results;
    }

Whereas ThriftClient is looking for SubTypes and creates the Entities with this information:

    public List<Object> findByRelation(String colName, Object colValue, Class entityClazz) {

            ...

            if (keySlices != null)
            {
                entities = new ArrayList<Object>(keySlices.size());

                MetamodelImpl metaModel = (MetamodelImpl) kunderaMetadata.getApplicationMetadata().getMetamodel(
                        m.getPersistenceUnit());

                EntityType entityType = metaModel.entity(m.getEntityClazz());

                List<AbstractManagedType> subManagedType = ((AbstractManagedType) entityType).getSubManagedType();

                if (subManagedType.isEmpty())
                {
                    entities = populateData(m, keySlices, entities, m.getRelationNames() != null, m.getRelationNames());
                }
                else
                {
                    for (AbstractManagedType subEntity : subManagedType)
                    {
                        EntityMetadata subEntityMetadata = KunderaMetadataManager.getEntityMetadata(kunderaMetadata,
                                subEntity.getJavaType());
                        entities = populateData(subEntityMetadata, keySlices, entities,
                                subEntityMetadata.getRelationNames() != null, subEntityMetadata.getRelationNames());
                        // TODOO:: if(entities != null)

                    }
                }
            }
        }
        return entities;
    }

[devender-yadav]

@Angoth you are right. Implementation for inheritance is not there for DS driver. I am working on it. I need to handle find, query, and relations. Will update you once I make those changes.

You can also contribute this feature if you like to work on it.

[Angoth]

I thought about it and looked into it but I'm rather busy at the moment, sorry. So I will wait for your solution :)

[devender-yadav]

Sure 👍