Our data model is separated into schemas on two databases. The schemas are utilized in isolation aside from a couple of single-key associations that bridge between your two. You will find no write transactions which will span both databases.

Such as this question Doing a join over 2 tables in different databases using Hibernate, you want to use Hibernate to deal with joining the organizations. We can't make use of the database solution (Federated sights on DB2).

We've setup Hibernate with two separate database designs (Physician and Patient), which works perfectly when utilizing DAOs to clearly access a specific session.

You want to use Hibernate to instantly retrieve the entity whenever we call DoctorBO.getExam().getPatient() Where examination consists of an id pointing towards the Patient table alternatively database.

One of the ways I have attempted carrying this out is applying a custom UserType:

public class DistributedUserType implements UserType, ParameterizedType
{
    public static final String CLASS = "CLASS";
    public static final String SESSION = "SESSION";

    private Class<? extends DistributedEntity> returnedClass;
    private String session;

    /** {@inheritDoc} */
    @Override
    public int[] sqlTypes()
    {
        // The column will only be the id
        return new int[] { java.sql.Types.BIGINT };
    }

    /** {@inheritDoc} */
    @Override
    public Class<? extends DistributedEntity> returnedClass()
    {
        // Set by typedef parameter
        return returnedClass;
    }

    /** {@inheritDoc} */
    @Override
    public boolean equals(Object x, Object y) throws HibernateException
    {
        if (x == y)
        {
            return true;
        }

        if ((x == null) || (y == null))
        {
            return false;
        }

        Long xId = ((DistributedEntity) x).getId();
        Long yId = ((DistributedEntity) y).getId();

        if (xId.equals(yId))
        {
            return true;
        }
        else
        {
            return false;
        }
    }

    /** {@inheritDoc} */
    @Override
    public int hashCode(Object x) throws HibernateException
    {
        assert (x != null);
        return x.hashCode();
    }

    /** {@inheritDoc} */
    @Override
    public Object nullSafeGet(ResultSet rs, String[] names, Object owner) throws HibernateException, SQLException
    {
        Long id = rs.getLong(names[0]);
        return HibernateUtils.getSession(session).get(returnedClass, id);
    }

    /** {@inheritDoc} */
    @Override
    public void nullSafeSet(PreparedStatement st, Object value, int index) throws HibernateException, SQLException
    {
        DistributedEntity de = (DistributedEntity) value;
        st.setLong(index, de.getId());
    }

    /** {@inheritDoc} */
    @Override
    public Object deepCopy(Object value) throws HibernateException
    {
        return value;
    }

    /** {@inheritDoc} */
    @Override
    public boolean isMutable()
    {
        return false;
    }

    /** {@inheritDoc} */
    @Override
    public Serializable disassemble(Object value) throws HibernateException
    {
        return (Serializable) value;
    }

    /** {@inheritDoc} */
    @Override
    public Object assemble(Serializable cached, Object owner) throws HibernateException
    {
        return cached;
    }

    /** {@inheritDoc} */
    @Override
    public Object replace(Object original, Object target, Object owner) throws HibernateException
    {
        return original;
    }

    /** {@inheritDoc} */
    @Override
    public void setParameterValues(Properties parameters)
    {
        String clazz = (String) parameters.get(CLASS);
        try
        {
            returnedClass = ReflectHelper.classForName(clazz);
        }
        catch (ClassNotFoundException e)
        {
            throw new IllegalArgumentException("Class: " + clazz + " is not a known class type.");
        }

        session = (String) parameters.get(SESSION);
    }
}

Which may then be utilized:

@TypeDef(name = "testUserType", typeClass = DistributedUserType.class, parameters = {
                                                                                 @Parameter(name = DistributedUserType.CLASS, value = PatientBO.CLASSNAME),
                                                                                 @Parameter(name = DistributedUserType.SESSION, value = HibernateUtils.PATIENT_SESS) })

@Type(type = "testUserType")
@Column(name = "PATIENT_ID")
private PatientBO patient;

The UserType works - the information is loaded properly with just the Id from the area endured towards the database. I've examined quite simple good examples of doctor.getExam().getPatient() and doctor.getExam().setPatient() and both appear to operate great, however think this can be a terrible hack and I don't have sufficient understanding of Hibernate to understand if this sounds like dependable.

It is possible to better method to achieve what we should want? May be the way I have referred to here sufficient, or does it cause difficulties later on?