HSQLDB example source code file (GroupedResult.java)

This example HSQLDB source code file (GroupedResult.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - HSQLDB tags/keywords

groupedresult, groupedresult, hashset, iterator, object, object, result, result, resultgroup, resultgroup

The HSQLDB GroupedResult.java source code

/* Copyright (c) 2001-2008, The HSQL Development Group
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of the HSQL Development Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG,
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


package org.hsqldb;

import org.hsqldb.lib.ArrayUtil;
import org.hsqldb.lib.HashSet;
import org.hsqldb.lib.Iterator;

/**
 * This class is used for grouping select results, especially for select
 * statements that include group by clause and nested aggregate functions.
 * It is used by the <b>Select class regardless the existence of group by
 * clause.
 * <p>
 * When a group by clause is defined, a <b>ResultGroup is used to hold
 * all column values and <b>AggregatingValues for each group.  When a group
 * by clause is not defined, one <b>ResultGroup is used to hold all the
 * results.<p>
 *
 * All <b>ResultGroups are placed in a HashSet.  Adding a new row
 * will first retrieve the corresponding group from the table, based on the
 * values in the group by columns.  If a group is found, then the row
 * associated with the group will be returned.  Otherwise a new group is
 * created with the new row, and the new row is returned.
 * <p>
 * The <b>Select can then update the values and AggregatingValues
 * in the returned row, rather than the original row.  This approach enables
 * nested aggregate functions, such as "count(id)+2, 20-count(id),
 * max(id)-min(id)" support.
 *
 * @author  Tony Lai
 * @version   1.7.2
 * @since   1.7.2
 * @see     Expression
 * @see     Select
 */

// fredt@users - patch 1.7.2 - mods to use new HashSet class and to separate addRow and getRow operations
class GroupedResult {

/** @todo fredt - initialise results on first use */
    private Result        result;
    int                   groupBegin;
    int                   groupEnd;
    private final boolean isGrouped;
    private final boolean isAggregated;
    private HashSet       groups;
    private ResultGroup   currGroup;

    GroupedResult(Select select, Result.ResultMetaData meta) {

        result       = new Result(meta);
        groupBegin   = select.iResultLen;
        groupEnd     = groupBegin + select.iGroupLen;
        isGrouped    = groupBegin != groupEnd;
        isAggregated = select.isAggregated;

        if (isGrouped) {
            groups = new HashSet();
        }
    }

    Object[] getRow(Object[] row) {

        if (isGrouped) {
            ResultGroup newGroup = new ResultGroup(row);
            ResultGroup group    = (ResultGroup) groups.get(newGroup);

            if (group != null) {
                ArrayUtil.copyArray(group.row, row, row.length);
            }
        } else if (isAggregated) {
            if (currGroup != null) {
                ArrayUtil.copyArray(currGroup.row, row, row.length);
            }
        }

        return row;
    }

    void addRow(Object[] row) {

        if (isGrouped) {
            ResultGroup newGroup = new ResultGroup(row);

            currGroup = (ResultGroup) groups.get(newGroup);

            if (currGroup == null) {
                currGroup = newGroup;

                groups.add(currGroup);
                result.add(row);
            } else {
                System.arraycopy(row, 0, currGroup.row, 0, row.length);
            }
        } else if (isAggregated) {
            if (currGroup == null) {
                currGroup = new ResultGroup(row);

                result.add(row);
            } else {
                System.arraycopy(row, 0, currGroup.row, 0, row.length);
            }
        } else {
            result.add(row);
        }
    }

    int size() {
        return result.getSize();
    }

    Iterator iterator() {
        return result.iterator();
    }

    Result getResult() {
        return result;
    }

    class ResultGroup {

        Object[] row;
        int      hashCode;

        private ResultGroup(Object[] row) {

            this.row = row;
            hashCode = 0;

            for (int i = groupBegin; i < groupEnd; i++) {
                if (row[i] != null) {
                    hashCode += row[i].hashCode();
                }
            }
        }

        public int hashCode() {
            return hashCode;
        }

        public boolean equals(Object obj) {

            if (obj == this) {
                return true;
            }

            if (obj == null ||!(obj instanceof ResultGroup)) {
                return false;
            }

            ResultGroup group = (ResultGroup) obj;

            for (int i = groupBegin; i < groupEnd; i++) {
                if (!equals(row[i], group.row[i])) {
                    return false;
                }
            }

            return true;
        }

        private boolean equals(Object o1, Object o2) {
            return (o1 == null) ? o2 == null
                                : o1.equals(o2);
        }
    }
}