odmg.java

用Java写的面相对象的数据库管理系统

// You can redistribute this software and/or modify it under the terms of
// the Ozone Library License version 1 published by ozone-db.org.
//
// The original code and portions created by SMB are
// Copyright (C) 1997-2000 by SMB GmbH. All rights reserved.
//
// $Id: ODMG.java,v 1.4 2000/10/28 16:55:19 daniela Exp $

package org.ozoneDB.odmg;

import java.io.*;
import org.odmg.*;
import org.ozoneDB.DxLib.*;


/**
 * This abstract class enhances the original ODMG {@link Implementation} interface
 * by a standard way to obtain the database of a given object. The newly
 * introduced static method allows to obtain the database for a given object
 * without the need to know the actual {@link Implementation} factory object. This
 * is particularly useful for ozone, where database object do not have access to
 * the client side logic and variables.<p>
 * 
 * {@link OzoneODMG} does already implement this interface. Wrappers for other
 * ODMG database systems just need to make sure to call the default ctor of the
 * underlying class.
 * 
 * 
 * @author <a href="http://www.softwarebuero.de/">SMB</a> @version
 * $Revision: 1.4 $Date: 2000/10/28 16:55:19 $
 */
public abstract class ODMG implements Implementation {
    
    private static DxBag factories;
    
    private static EnhDatabase theServerSideODMGDatabase;
    
    
    static {
        // are we inside the server...
        if (org.ozoneDB.core.Env.currentEnv() != null) {
            theServerSideODMGDatabase = new OzoneServerODMGDatabase();
        } else {
            // ...or inside the client
            factories = new DxArrayBag();
        } 
    } 
    
    
    public static Database getDatabase2( Object obj ) {
        // are we inside the server...
        if (theServerSideODMGDatabase != null) {
            return theServerSideODMGDatabase;
        } else {
            // ...or inside the client
            ODMG odmg = null;
            DxIterator it = factories.iterator();
            while ((odmg = (ODMG)it.next()) != null) {
                Database db = odmg.getDatabase( obj );
                if (db != null) {
                    return db;
                } 
            } 
            return null;
        } 
    } 
    
    
    public ODMG() {
        factories.add( this );
    }
    
}