Object explorer cannot open odb file. ObjectDB many-to-many relationship

#1

I created a data model to test many-to-many relationship with a link table as following (full code in attachement)

@Entity
public class User {
    @Id
    private String code;

    @OneToMany(mappedBy = "user") @MapKey
    private Map<Assignement.PK, Assignement> assignements;
}

@Entity
public class Project {
    @Id
    private String code;
   
    @OneToMany(mappedBy = "project") @MapKey
    private Map<Assignement.PK, Assignement> assignements;
}

@Entity @IdClass(Assignement.PK.class)
public class Assignement
{
    @Id @ManyToOne(cascade = CascadeType.ALL, optional = false)
    private User user;
   
    @Id @ManyToOne(cascade = CascadeType.ALL, optional = false)
    private Project project;
   
    @Embeddable
    public static class PK
    {
        public String user;
        public String project;
       
        public PK(User user, Project project)
        {
            this.user = user.getCode();
            this.project = project.getCode();
        }
    }
}

The following test passed OK, everything is as expected

   EntityManager em = EMF.get().createEntityManager();

   User u1 = new User("u1");
   User u2 = new User("u2");
   Project p1 = new Project("p1");
   Project p2 = new Project("p2");
  
   em.getTransaction().begin();
   em.persist(p1);
   em.persist(p2);
   em.persist(u1);
   em.persist(u2);
   em.persist(new Assignement(u1, p1));
   em.persist(new Assignement(u1, p2));
   em.persist(new Assignement(u2, p1));
   em.getTransaction().commit();
  
   assertNull(u1.getAssignements());
   em.refresh(u1); ///fetch the Assignements collection of u1
   assertNotNull(u1.getAssignements());
  
   int countProjectsAssignedToU1 = u1.getAssignements().keySet().toArray().length;
   assertEquals(2, countProjectsAssignedToU1);
  
   //prouve that we can access the project p1 through u1.Assignements
   Assignement.PK a11pk = new Assignement.PK(u1, p1);
   Assignement a11 = u1.getAssignements().get(a11pk);
   assertEquals(p1, a11.getProject());

But:

Question 1: After my test, the database file is created (in attachement) but I cannot open it with ObjectDB Explorer (Message: "Cannot open file 'demo.odb' null"). 

Note: I'm using Windows 7 64 bits. jdk1.6.0_27. ObjectDB doctor did not find any anormalie in the file

I found the following log file:

java.lang.NullPointerException
at com.objectdb.jpa.type.IdentifiableTypeImpl.initAttributes(IdentifiableTypeImpl.java:110)
at com.objectdb.jpa.MetamodelImpl.obtainType(MetamodelImpl.java:290)
at com.objectdb.jpa.type.ManagedTypeImpl.newAttribute(ManagedTypeImpl.java:112)
at com.objectdb.jpa.type.ManagedTypeImpl.initAttributes(ManagedTypeImpl.java:91)
at com.objectdb.jpa.type.IdentifiableTypeImpl.initAttributes(IdentifiableTypeImpl.java:82)
at com.objectdb.jpa.MetamodelImpl.obtainType(MetamodelImpl.java:290)
at com.objectdb.jpa.MetamodelImpl.prepareTypeLists(MetamodelImpl.java:228)
at com.objectdb.jpa.MetamodelImpl.getManagedTypes(MetamodelImpl.java:98)
at com.objectdb.o.EHL.d(EHL.java:56)
at com.objectdb.o.MTI.<init>(MTI.java:39)
at com.objectdb.o.SCP.h(SCP.java:126)
at com.objectdb.o.MFR.j(MFR.java:235)
at com.objectdb.o.MFR.j(MFR.java:233)
at com.objectdb.o.MFR.j(MFR.java:233)
at com.objectdb.o.MFR.j(MFR.java:233)
at com.objectdb.o.MFR.i(MFR.java:218)
at com.objectdb.o.EXA.o(EXA.java:194)
at com.objectdb.o.EXA.n(EXA.java:186)
at com.objectdb.o.CNC.g(CNC.java:117)
at com.objectdb.o.EXA.<init>(EXA.java:79)
at com.objectdb.Explorer$1.run(Explorer.java:53)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:641)
at java.awt.EventQueue.access$000(EventQueue.java:84)
at java.awt.EventQueue$1.run(EventQueue.java:602)
at java.awt.EventQueue$1.run(EventQueue.java:600)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:611)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:269)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:184)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:174)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:169)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)

Question 2: All test passe. Howrever, can you tell me: Is my above implementation alright for objectDB?

I'd like to implement a many-to-many relationship so that User and Project can be directly access from Assignement (not by theirs key), and we can easily get an Assignement object from User object and Underlying object (but not through theirs keys).

I'd like to work with typed object in the code whenever possible, and make key usage as transparent as possible. The implementation above response to what I want, but I don't know if it is alright in ObjectDB. Do you have any advises/suggestion?

Regards.

application/zip icondemoObjectDB.zip (4.15KB)
test example many-to-many relationship User, Project, Assignement
#2

There was a bug in the Explorer. The many-to-many relationship wasn't the problem but the id class. Anyway, build 2.3.4 fixes this bug and now your sample database can be opened in the Explorer.

You can use many-to-many bidirectional relationships with ObjectDB. Just be aware that navigation from the mapped by (inverse) side to the owner side is slower since it requires query execution.

Usually you can get better performance by using two unidirectional relationships (with no mapped by). You will have to maintain both sides, but navigation may be faster since no queries will be required. This ability (of navigation in the to many direction with no queries) is not supported by ORM JPA implementations, so you will be leveraging the performance advantage of ObjectDB.

ObjectDB Support
ObjectDB - Fast Object Database for Java (JPA/JDO)

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