001/*
002 * #%L
003 * Netarchivesuite - harvester
004 * %%
005 * Copyright (C) 2005 - 2014 The Royal Danish Library, the Danish State and University Library,
006 *             the National Library of France and the Austrian National Library.
007 * %%
008 * This program is free software: you can redistribute it and/or modify
009 * it under the terms of the GNU Lesser General Public License as
010 * published by the Free Software Foundation, either version 2.1 of the
011 * License, or (at your option) any later version.
012 * 
013 * This program is distributed in the hope that it will be useful,
014 * but WITHOUT ANY WARRANTY; without even the implied warranty of
015 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
016 * GNU General Lesser Public License for more details.
017 * 
018 * You should have received a copy of the GNU General Lesser Public
019 * License along with this program.  If not, see
020 * <http://www.gnu.org/licenses/lgpl-2.1.html>.
021 * #L%
022 */
023package dk.netarkivet.harvester.datamodel.extendedfield;
024
025import java.util.List;
026
027import dk.netarkivet.harvester.datamodel.DAO;
028
029/**
030 * Interface for creating and accessing extended fields in persistent storage.
031 */
032public abstract class ExtendedFieldTypeDAO implements DAO {
033
034    /** The database singleton model. */
035    protected static ExtendedFieldTypeDAO instance;
036
037    /**
038     * constructor used when creating singleton. Do not call directly.
039     */
040    protected ExtendedFieldTypeDAO() {
041    }
042
043    /**
044     * Reset the DAO instance. Only for use from within tests.
045     */
046    protected static void reset() {
047        instance = null;
048    }
049
050    /**
051     * Tests if exists an ExtendedFieldType with the given ID.
052     *
053     * @param aExtendedfieldtypeId An id belonging to an ExtendedFieldType
054     * @return true, if there exists an ExtendedFieldType with the given ID, otherwise returns false.
055     */
056    public abstract boolean exists(Long aExtendedfieldtypeId);
057
058    /**
059     * Read an ExtendedFieldType belonging to the given id.
060     *
061     * @param aExtendedfieldtypeId an id belonging to a ExtendedFieldType
062     * @return an ExtendedFieldType from belonging to the given id.
063     */
064    public abstract ExtendedFieldType read(Long aExtendedfieldtypeId);
065
066    /**
067     * @return a list of all ExtendedFieldTypes.
068     */
069    public abstract List<ExtendedFieldType> getAll();
070
071    /**
072     * If an instance exists, return it, otherwise instantiate one, and return it.
073     *
074     * @return the instance of this class.
075     */
076    public static synchronized ExtendedFieldTypeDAO getInstance() {
077        if (instance == null) {
078            instance = new ExtendedFieldTypeDBDAO();
079        }
080        return instance;
081    }
082
083}