Quadcap Embeddable Database

com/quadcap/sql/JoinCursor.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.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;

import java.util.Hashtable;
import java.util.Vector;

import java.sql.SQLException;

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

import com.quadcap.util.Debug;

/**
 * Cursor implementation of cross-join (cartesion product)
 *
 * @author Stan Bailes
 */
public abstract class JoinCursor extends CursorImpl {
    Cursor                              ca;
    Cursor                              cb;
    JoinMapRow                          row;
    Expression                          where;
    boolean                             left;
    boolean                             inner;

    Row                                 ra;
    Row                                 rb;
    Expression                          aWhere;

    public JoinCursor(Session session, Cursor outer, Cursor ca, Cursor cb,
                      Expression where, Tuple tuple, JoinMapRow row,
                      boolean left, boolean inner)
        throws SQLException
    {
        super(session, null, outer);
        this.ca = ca;
        this.cb = cb;
        addColumns(session, tuple);
        // XXX This is the problem.  It's not the fact that the rows
        // XXX are flipped, per se, it's just that the key fields
        // XXX must be in the outer, rather than the inner row.
        // XXX So flip() must know what the key fields are in each
        // XXX row.
        this.row = row;
        this.where = where;
        this.left = left;
        this.inner = inner;

        if (!(ca instanceof JoinCursor)) {
            this.aWhere = new Analyze(session, where).factorTable(ca);
        }

        //Debug.println("ca = " + ca.getClass().getName() + ": " + ca);
        //Debug.println("cb = " + cb.getClass().getName() + ": " + cb);
    }

    public Row getRow() {
        return row;
    }

    public void updateRow(Row row) throws SQLException {
        throw new SQLException("JOIN cursors not updateable", "42000");
    }

    public void deleteRow() throws SQLException {
        throw new SQLException("JOIN cursor: delete not supported", "42000");
    }

    public void afterLast() throws SQLException {
        throw new SQLException("JOIN cursor: afterLast not supported",
                               "42000");
    }

    public boolean isWritable(int column) { return false; }

    public void beforeFirst() throws SQLException {
        ca.beforeFirst();
        cb.beforeFirst();
        ra = null;
        row.setA(null);
        rb = null;
        row.setB(null);
    }

    protected boolean anext() throws SQLException {
        boolean ret = ca.next();
        while (ret && !passRow(ca, aWhere)) {
            ret = ca.next();
        }
        if (ret) {
            ra = ca.getRow();
        } else {
            ra = null;
        }
        row.setA(ra);
        //Debug.println("anext: ra = " + ra + ", row = " + row);
        return ret;
    }

    protected void bfirst() throws SQLException {
        cb.beforeFirst();
    }

    protected boolean bnext() throws SQLException {
        boolean ret = cb.next();
        if (ret) {
            rb = cb.getRow();
        } else {
            rb = null;
        }
        row.setB(rb);
        //Debug.println("bnext: rb = " + rb + ", row = " + row);
        return ret;
    }

    public boolean next() throws SQLException {
        boolean ret = false;
        while (ra != null && !ret && inner && bnext()) {
            ret = true;
        }
        if (!ret) {
            while (anext()) {
                boolean anyInner = false;
                bfirst();
                while (bnext()) {
                    anyInner = true;
                    if (inner) {
                        return true; // single exit is "inconvenient"
                    }
                }
                if (left && !anyInner) {
                    ret = true;
                    break;
                }
            }
        }
        return ret;
    }    

    final boolean passRow(Cursor c, Expression w)
        throws SQLException
    {
        boolean ret = true;
        if (w != null) {
            Value val = w.getValue(session, c);
            if (val instanceof ValueBoolean) {
                ValueBoolean vb = (ValueBoolean)val;
                ret = vb.isTrue();
            } else {
                ret = false;
            }
        }
        return ret;
    }

    public void close() throws SQLException {
        SQLException ex = null;
        try {
            ca.close();
        } catch (SQLException e) {
            ex = e;
        } finally {
            ca = null;
            try {
                cb.close();
            } catch (SQLException e) {
                if (ex != null) ex = e;
            } finally {
                cb = null;
            }
        }
        if (ex != null) throw ex;
    }
        
    public long size() throws SQLException { return -1; }
}