/**
 * A PersistentSet represents a group of Persistent objects
 * based on certain query criteria.
 */
package imaginary.persist;

import java.rmi.RemoteException;
import java.util.Hashtable;
import java.util.Vector;

public abstract class PersistentSet extends imaginary.util.Observable
implements RemotePersistentSet {
    /****************** Instance attributes ****************/
    // objects in the set
    private Vector      objects     = new Vector(); 

    /******************** Constructors *********************/
    /**
     * Creates a new PersistentSet.
     */
    public PersistentSet() throws RemoteException {
        super();
    }

    /**************** Attribute accessors ******************/
    /**
     * Called by its peer to add a restored Persistent to the set.
     * @param p the Persistent to be added to the set
     */
    public synchronized void addPersistent(Persistent p) {
        if( !objects.contains(p) ) {
            objects.addElement(p);
        }
    }

    /**
     * Allows external objects to get a list of the Persistent objects
     * in this set.
     * @return the Persistent objects in the set
     */
    public synchronized RemotePersistent[] getPersistents() {
        RemotePersistent[] persistents = new RemotePersistent[objects.size()];

        objects.copyInto(persistents);
        return persistents;
    }

    /**
     * Subclasses must implement this method in order to tell
     * this class what to use for a PersistentSetPeer.
     * @return the peer for this set
     */
    protected abstract PersistentSetPeer getPersistentSetPeer();

    /***************** Persistence operations ****************/
    /**
     * Loads the set without any query criteria.  In other words,
     * it loads all objects of a given type.
     * @exception imaginary.persist.PersistenceException An error occurred
     * in accessing the database.
     */
    public synchronized void restore() throws PersistenceException {
        Transaction t = Transaction.getTransaction();

        t.restore(this, null);
    }

    /**
     * Loads a set of persistent objects based on query criteria listed in
     * a the Hashtable values.
     * @param h the values for filtering the objects of a specific type
     * @exception imaginary.persist.PersistenceException An error occurred
     * in accessing the database.
     */
    public synchronized void restore(Hashtable h) throws PersistenceException {
        Transaction t = Transaction.getTransaction();

        t.restore(this, h);
    }

    /**
     * Loads a set of persistent objects based on query criteria listed in
     * a the Hashtable values.
     * @param trans the Transaction object to use for the restore
     * @param data the values for filtering the objects of a specific type
     * @exception imaginary.persist.PersistenceException An error occurred
     * in accessing the database.
     */
    public synchronized void restore(Transaction trans, Hashtable data)
    throws PersistenceException {
        getPersistentSetPeer().restore(this, trans, data);
    }
}