Quadcap Embeddable Database

com/quadcap/sql/PredicateCursor.java

Go to the documentation of this file.

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.util.Vector;

import java.sql.SQLException;

import com.quadcap.sql.types.Value;
import com.quadcap.sql.types.ValueBoolean;
import com.quadcap.sql.types.ValueUnknown;

import com.quadcap.util.Debug;

/**
 * Cursor for <b>WHERE</b> predicates.
 *
 * @author Stan Bailes
 */
public class PredicateCursor extends FilterCursor {
    Expression  predicate                       = null;
    Row         row                             = null;

    /**
     * A PredicateCursor is a kind of FilterCursor which only returns
     * rows which match a predicate
     */
    public PredicateCursor(Session session, Cursor cursor,
                           Expression predicate) throws SQLException {
        super(session, cursor);
        this.predicate = predicate;
    }

    /**
     * Return the current cursor row
     */
    public Row getRow() throws SQLException {
        return row;
    }

    /**
     * Cursor.next()  Advance the cursor and return 'true' if the cursor
     * advances past a valid item.  This item becomes the current row.
     */
    public boolean next() throws SQLException {
        row = null;
        while (row == null && cursor.next()) {
            Value val = predicate.getValue(session, cursor);
            //Debug.println("[" + predicate + "] on " + cursor.getRow() + "  " +
            //             (outer == null ? "{}" : outer.getRow().toString()) + " = " + val);
            if (Value.isTrue(val)) {
                row = cursor.getRow();
            }
        }
        return row != null;
    }

    /**
     * Cursor.next()  Retreat the cursor and return 'true' if the cursor
     * moves past a valid item.  This item becomes the current row.
     */
    public boolean prev() throws SQLException {
        row = null;
        while (row == null && cursor.prev()) {
            Value val = predicate.getValue(session, cursor);
            if (Value.isTrue(val)) {
                row = cursor.getRow();
            }
        }
        return row != null;
    }

    /**
     * Position the cursor to the specified absolute row.  The first row
     * is row '1', and the last row is '-1', as in JDBC.
     */
    public boolean absolute(int row) throws SQLException {
        if (row > 0) {
            beforeFirst();
            while (row-- > 0) if (!next()) return false;
        } else {
            afterLast();
            while (row++ < 0) if (!prev()) return false;
        }
        return true;
    }

    
    //#ifdef DEBUG
    public String toString() {
        return "PredicateCursor: " + super.toString();
    }
    //#endif
    
}