Quadcap Embeddable Database

com/quadcap/sql/BC_Cursor.java

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package com.quadcap.sql;

/* Copyright 1999 - 2003 Quadcap Software.  All rights reserved.
 *
 * This software is distributed under the Quadcap Free Software License.
 * This software may be used or modified for any purpose, personal or
 * commercial.  Open Source redistributions are permitted.  Commercial
 * redistribution of larger works derived from, or works which bundle
 * this software requires a "Commercial Redistribution License"; see
 * http://www.quadcap.com/purchase.
 *
 * Redistributions qualify as "Open Source" under  one of the following terms:
 *   
 *    Redistributions are made at no charge beyond the reasonable cost of
 *    materials and delivery.
 *
 *    Redistributions are accompanied by a copy of the Source Code or by an
 *    irrevocable offer to provide a copy of the Source Code for up to three
 *    years at the cost of materials and delivery.  Such redistributions
 *    must allow further use, modification, and redistribution of the Source
 *    Code under substantially the same terms as this license.
 *
 * Redistributions of source code must retain the copyright notices as they
 * appear in each source code file, these license terms, and the
 * disclaimer/limitation of liability set forth as paragraph 6 below.
 *
 * Redistributions in binary form must reproduce this Copyright Notice,
 * these license terms, and the disclaimer/limitation of liability set
 * forth as paragraph 6 below, in the documentation and/or other materials
 * provided with the distribution.
 *
 * The Software is provided on an "AS IS" basis.  No warranty is
 * provided that the Software is free of defects, or fit for a
 * particular purpose.  
 *
 * Limitation of Liability. Quadcap Software shall not be liable
 * for any damages suffered by the Licensee or any third party resulting
 * from use of the Software.
 */

import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

import java.sql.SQLException;

import com.quadcap.sql.io.ObjectInputStream;
import com.quadcap.sql.io.ObjectOutputStream;

import com.quadcap.sql.file.SubPageManager;
import com.quadcap.sql.index.BCursor;

import com.quadcap.util.Debug;

/**
 * Cursor that implements the <b>DISTINCT</b> modifier by creating
 * temporary table, where the entire row is used as the index key.
 *
 * @author Stan Bailes
 */
public abstract class BC_Cursor extends CursorImpl {
    protected BCursor                    bc              = null;
    protected LazyRow                    row             = null;
    protected boolean                    rowValid        = false;
    protected long                       rowId           = 0;

    /**
     * Constructor on session and cursor
     */
    public BC_Cursor(Session session, String name, Cursor outer)
        throws SQLException
    {
        super(session, name, outer);
    }

    /**
     * Cursor.getRow(): return the current table row, fetching it if necessary
     * based on the rowId
     */
    public Row getRow() throws SQLException {
        Row ret = null;
        if (rowId != 0) {
            if (!rowValid) {
                try {
                    fetchCurrentRow();
                } catch (IOException ex) {
                    throw DbException.wrapThrowable(ex);
                }
            }
            if (rowValid) {
                ret = row;
            }
        }
        return row;
    }

    /**
     * Make the row too, while you're at it...
     */
    public abstract void checkCursor() throws IOException, SQLException;

    public abstract long getCurrentRowId() throws IOException, SQLException;

    public abstract void fetchCurrentRow() throws IOException, SQLException;
    
    public boolean isWritable(int column) { return false; }

    public boolean absolute(int x) throws SQLException {
        try {
            rowValid = false;
            rowId = 0;
            checkCursor();
            boolean ret = bc.absolute(x);
            if (ret) {
                rowId = getCurrentRowId();
            }
            return ret;
        } catch (IOException e) {
            throw DbException.wrapThrowable(e);
        }
    }

    public void beforeFirst() throws SQLException {
        try {
            rowValid = false;
            rowId = 0;
            checkCursor();
            bc.beforeFirst();
        } catch (IOException e) {
            throw DbException.wrapThrowable(e);
        }
    }

    public void afterLast() throws SQLException {
        try {
            rowValid = false;
            rowId = 0;
            checkCursor();
            bc.afterLast();
        } catch (IOException e) {
            throw DbException.wrapThrowable(e);
        }
    }

    public boolean next() throws SQLException {
        try {
            rowValid = false;
            rowId = 0;
            checkCursor();
            boolean ret = bc.next();
            if (ret) {
                rowId = getCurrentRowId();
            }
            return ret;
        } catch (IOException e) {
            throw DbException.wrapThrowable(e);
        }
    }

    public boolean prev() throws SQLException {
        try {
            rowValid = false;
            rowId = 0;
            checkCursor();
            boolean ret = bc.prev();
            if (ret) rowId = getCurrentRowId();
            return ret;
        } catch (IOException e) {
            throw DbException.wrapThrowable(e);
        }
    }

    /**
     * On close, we release the resources.
     */
    public void close() throws SQLException {
        try {
            if (bc != null) bc.release();
        } finally {
            bc = null;
            row = null;
        }
    }

    /**
     * Return the row id
     */
    public long getRowId() {
        return rowId;
    }

    /**
     * Return the size of the index backing this cursor.
     */
    public long size() throws SQLException {
        try {
            return bc.size();
        } catch (IOException e) {
            throw DbException.wrapThrowable(e);
        }
    }
    
    public void updateRow(Row row) throws SQLException {
        throw new SQLException("Cursor not updateable");
    }

    public void deleteRow() throws SQLException {
        throw new SQLException("Cursor not updateable");
    }
}