IllegalArgumentException: expecting IdClass mapping

Question

During deploying my app I occurs on that exception. I have a lot of class in my app and I dont know where I must to place @IdClass and what does this exception mean anyway. I am using Hibernate 4.1 and JBoss AS 7.1

12:10:23,761 INFO  [org.hibernate.engine.jdbc.internal.LobCreatorBuilder] (MSC service thread 1-5) HHH000424: Disabling contextual LOB creation as createClob() method threw error : java.lang.reflect.InvocationTargetException
12:10:24,075 ERROR [org.hibernate.tool.hbm2ddl.SchemaExport] (MSC service thread 1-5) HHH000389: Unsuccessful: drop sequence hibernate_sequence
12:10:24,076 ERROR [org.hibernate.tool.hbm2ddl.SchemaExport] (MSC service thread 1-5) ERROR: sequence "hibernate_sequence" does not exist
12:10:24,281 ERROR [org.jboss.msc.service.fail] (MSC service thread 1-5) MSC00001: Failed to start service jboss.persistenceunit."kladr.ear/kladr-ejb-1.0-SNAPSHOT.jar#primary": org.jboss.msc.service.StartException in service jboss.persistenceunit."kladr.ear/kladr-ejb-1.0-SNAPSHOT.jar#primary": Failed to start service
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1767) [jboss-msc-1.0.2.GA.jar:1.0.2.GA]
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886) [rt.jar:1.6.0_35]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908) [rt.jar:1.6.0_35]
    at java.lang.Thread.run(Thread.java:662) [rt.jar:1.6.0_35]
Caused by: java.lang.IllegalArgumentException: expecting IdClass mapping
    at org.hibernate.ejb.metamodel.AttributeFactory$3.resolveMember(AttributeFactory.java:878)
    at org.hibernate.ejb.metamodel.AttributeFactory$4.resolveMember(AttributeFactory.java:915)
    at org.hibernate.ejb.metamodel.AttributeFactory.determineAttributeMetadata(AttributeFactory.java:423)
    at org.hibernate.ejb.metamodel.AttributeFactory.buildAttribute(AttributeFactory.java:91)
    at org.hibernate.ejb.metamodel.MetadataContext.wrapUp(MetadataContext.java:214)
    at org.hibernate.ejb.metamodel.MetamodelImpl.buildMetamodel(MetamodelImpl.java:64)
    at org.hibernate.ejb.EntityManagerFactoryImpl.<init>(EntityManagerFactoryImpl.java:91)
    at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:904)
    at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:889)
    at org.hibernate.ejb.HibernatePersistence.createContainerEntityManagerFactory(HibernatePersistence.java:73)
    at org.jboss.as.jpa.service.PersistenceUnitServiceImpl.createContainerEntityManagerFactory(PersistenceUnitServiceImpl.java:162)
    at org.jboss.as.jpa.service.PersistenceUnitServiceImpl.start(PersistenceUnitServiceImpl.java:85)
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.startService(ServiceControllerImpl.java:1811) [jboss-msc-1.0.2.GA.jar:1.0.2.GA]
    at org.jboss.msc.service.ServiceControllerImpl$StartTask.run(ServiceControllerImpl.java:1746) [jboss-msc-1.0.2.GA.jar:1.0.2.GA]
    ... 3 more

Answer 1

@IdClass annotation is used to define the Class that contains the id. i.e. This is generally used in case defining a compound key. i.e. a key composite of more than one attribute. If that is the case, than this is how we do. take a look at following example.. we define a class as IdClass and use @Id's to define varrious Ids for thisIdClass`.

Example :

@Entity
@IdClass(AssignedRoleId.class)
public class AssignedRole
{
  @Id
  @ManyToOne
  private User userId;

  @Id
  @ManyToOne  
  private Role roleId;

  private Date dateAssigned;
}

Hope this helps.

Answer 2

Elaborating further on @Mukul correct answer the @IdClass should have the following properties:

1. It should implement Serializable
2. It should have a constructor that takes the ids (i.e. the fields associated with @Id)
3. It should override equals and hashCode

It's sometime useful to make this class as a static inner class of the entity, here's an example:

@Entity 
@IdClass(AssignedRoleId.class)
public class AssignedRole
{ 
    @Id
    @ManyToOne
    private User userId;

    @Id
    @ManyToOne
    private Role roleId;

    private Date dateAssigned;

    public static class AssignedRoleId implements Serializable {

        private User userId;
        private Role roleId;

        public AssignedRoleId() {}

        public AssignedRoleId(User userId, Role roleId) {
            this.userId = userId;
            this.roleId = roleId;
        }

        @Override
        public boolean equals(Object o) {

            if (o == this) {
                return true;
            }
            if (!(o instanceof AssignedRole)) {
                return false;
            }
            AssignedRole assignedRole = (AssignedRole) o;
            return Objects.equals(userId, assignedRole.getUserId()) &&
                   Objects.equals(roleId, assignedRole.getRoleId());
        }

        @Override
        public int hashCode() {
            return Objects.hash(userId, roleId);
        }
   }
}