Date saved but retrieved null in ElementCollection (or Embedded) property

[mj3c]

I have an object of type Instance which contains an @ElementCollection of type Datapoint. Each datapoint has a timestamp and a value. In a test, I create some instances with their datapoints and save them, however, when I read any of those instances back from the database, the value for datapoints is set but the timestamp is null.

I am using:
Cassandra 3.11.2
Kundera 3.12

persistence.xml

    <persistence-unit name="cassandra_pu">
        <provider>com.impetus.kundera.KunderaPersistence</provider>
        <properties>
            <property name="kundera.nodes" value="localhost"/>
            <property name="kundera.port" value="9042"/>
            <property name="kundera.keyspace" value="d2lablite"/>
            <property name="kundera.dialect" value="cassandra"/>
            <property name="kundera.ddl.auto.prepare" value="create" />
            <property name="kundera.client.lookup.class" value="com.impetus.kundera.client.cassandra.dsdriver.DSClientFactory" />
        </properties>
    </persistence-unit>

Datapoint.java

@Embeddable
public class Datapoint {
    @Column(name="timestamp")
    @Temporal(TemporalType.TIMESTAMP)
    private java.util.Date timestamp;

    @Column(name="value")
    private double value;

    public Datapoint() { }

    // Getters, setters
}

Instance.java

@Entity
@Table(name="instances")
public class Instance {
    @Id
    @Column(name="uuid")
    private String uuid;

    @Column(name="param")
    private String param;

    @ElementCollection
    @Column(name="datapoints")
    private List<Datapoint> datapoints;

    @ElementCollection
    @Column(name="metadata")
    private Map<String, String> metadata;

    @Temporal(TemporalType.TIMESTAMP)
    @Column(name="date")
    private Date date;

    public Instance() { }
}

So what I do is:

• Create an Instance, create a List<Datapoint>, set it to instance and persist the instance
• Check via cqlsh that the instance is saved and all datapoints have the timestamp saved as well
• Use the EntityManager's find method to fetch an instance by its uuid, and it contains all values, including the date column, and its datapoints contain their values but the timestamp field in every datapoint is null.

I have also tried to use @Embedded and only 1 Datapoint instead of a list and the result is the same, timestamp is null.

What did I miss?

[devender-yadav]

Hi @milosjajac,

I will try to replicate this on Monday.

-Dev

[devender-yadav]

Hi @milosjajac, working fine for me.

public static void main(String[] args)
{

    Map<String, String> props = new HashMap<String, String>();
    props.put(CassandraConstants.CQL_VERSION, CassandraConstants.CQL_VERSION_3_0);
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("issue_pu", props);

    EntityManager em = emf.createEntityManager();

    Datapoint dp1 = new Datapoint();
    dp1.setValue(10.01);
    dp1.setTimestamp(new Date());

    Datapoint dp2 = new Datapoint();
    dp2.setValue(11.01);
    dp2.setTimestamp(new Date());

    List<Datapoint> list = new ArrayList<>();
    list.add(dp1);
    list.add(dp2);

    Instance instance = new Instance();
    instance.setDatapoints(list);
    instance.setDate(new Date());
    instance.setParam("some-param");

    String id = UUID.randomUUID().toString();

    instance.setUuid(id);

    em.persist(instance);
    Instance inst = em.find(Instance.class, id);

    List<Datapoint> dps = inst.getDatapoints();

    for (Datapoint datapoint : dps)
    {
        System.out.println(datapoint.getTimestamp());
    }

 }

[mj3c]

Thank you @devender-yadav for getting back to this.

I have tried your example and it does work when I use find() to retrieve a single instance, however, how would I do this to retrieve a list of instances from Cassandra?

• I have tried doing createNativeQuery("SELECT * FROM instances", Instance.class) but the datapoint timestamps are null (even though the instance date is loaded correctly).
• I have also tried createQuery("SELECT i FROM Instance i", Instance.class) but this yields an exception I found in another issue here, sadly without a solution.

One more thing I have noticed aside from this is that closing the EntityManager, getting a new one from the factory and trying find() on it leads to an exception with the message "undefined column name key", leading me to believe that for some reason the second EntityManager does not know that the id column is named "uuid". Should I never close the initial EntityManager and always use it instead?

I could not find any information on these two matters when reading the docs.

[devender-yadav]

Hi @milosjajac,

Seems like an issue from Kundera side.

[devender-yadav]

Hi @milosjajac,

This issue is fixed and will be available in the next Kundera release.