Question

I have class which has Map, but when I try to presist this entity, throws null pointer exception. What could be wrong in my code/settings?

My class:

@PersistenceCapable(detachable="true")
public class MyClassEntity implements MyClass {

    @PrimaryKey
    @Persistent(valueStrategy=IdGeneratorStrategy.NATIVE)
    private String id;

    @Persistent @Join @Element(embedded="true")
    @Extension(vendorName = "datanucleus", key = "implementation-classes", value = "com.company.MySecondClassEntity")
    private Map<String, MySecondClass> map = new HashMap<String, MySecondClass>();

    // Getters and setters here

}

Exception:

Exception in thread "main" java.lang.NullPointerException
    at org.datanucleus.store.rdbms.sql.AbstractStatementGenerator.<init>(AbstractStatementGenerator.java:101)
    at org.datanucleus.store.rdbms.sql.AbstractStatementGenerator.<init>(AbstractStatementGenerator.java:139)
    at org.datanucleus.store.rdbms.sql.UnionStatementGenerator.<init>(UnionStatementGenerator.java:153)
    at org.datanucleus.store.rdbms.scostore.RDBMSJoinMapStore.getSQLStatementForGet(RDBMSJoinMapStore.java:770)
    at org.datanucleus.store.rdbms.scostore.RDBMSJoinMapStore.getValue(RDBMSJoinMapStore.java:639)
    at org.datanucleus.store.rdbms.scostore.RDBMSJoinMapStore.putAll(RDBMSJoinMapStore.java:195)
    at org.datanucleus.store.mapped.mapping.MapMapping.postInsert(MapMapping.java:135)
    at org.datanucleus.store.rdbms.request.InsertRequest.execute(InsertRequest.java:520)
    at org.datanucleus.store.rdbms.RDBMSPersistenceHandler.insertTable(RDBMSPersistenceHandler.java:166)
    at org.datanucleus.store.rdbms.RDBMSPersistenceHandler.insertObject(RDBMSPersistenceHandler.java:142)
    at org.datanucleus.state.JDOStateManager.internalMakePersistent(JDOStateManager.java:2377)
    at org.datanucleus.state.JDOStateManager.makePersistent(JDOStateManager.java:2353)
    at org.datanucleus.ObjectManagerImpl.persistObjectInternal(ObjectManagerImpl.java:1896)
    at org.datanucleus.ObjectManagerImpl.persistObjectWork(ObjectManagerImpl.java:1745)
    at org.datanucleus.ObjectManagerImpl.persistObject(ObjectManagerImpl.java:1593)
    at org.datanucleus.api.jdo.JDOPersistenceManager.jdoMakePersistent(JDOPersistenceManager.java:731)
    at org.datanucleus.api.jdo.JDOPersistenceManager.makePersistent(JDOPersistenceManager.java:756)
    at com.mycompany.dao.impl.JDOGenericDao.save(JDOGenericDao.java:63)
    at com.mycompany.dao.Main.main(Main.java:29)

Maven dependecies:

 <dependencies>
    <dependency>
        <groupId>org.datanucleus</groupId>
        <artifactId>datanucleus-core</artifactId>
        <version>3.1.2</version>
    </dependency>
    <dependency>
        <groupId>org.datanucleus</groupId>
        <artifactId>datanucleus-api-jdo</artifactId>
        <version>3.1.2</version>
    </dependency>
    <dependency>
        <groupId>javax.jdo</groupId>
        <artifactId>jdo-api</artifactId>
        <version>3.0.1</version>
    </dependency>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>[1.2, 1.3)</version>
    </dependency>
    <dependency>
        <groupId>org.datanucleus</groupId>
        <artifactId>datanucleus-rdbms</artifactId>
        <version>3.1.2</version>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.21</version>
    </dependency>
</dependencies>

Answer 1

Would have thought that “value-implementation-classes” as an extension key makes way more sense than what you have there (otherwise how is it to know that you are talking about the values of the map and not the keys?)