001    /**
002     * Copyright (c) 2000-2013 Liferay, Inc. All rights reserved.
003     *
004     * This library is free software; you can redistribute it and/or modify it under
005     * the terms of the GNU Lesser General Public License as published by the Free
006     * Software Foundation; either version 2.1 of the License, or (at your option)
007     * any later version.
008     *
009     * This library is distributed in the hope that it will be useful, but WITHOUT
010     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
011     * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
012     * details.
013     */
014    
015    package com.liferay.portal.dao.orm.hibernate;
016    
017    import com.liferay.portal.kernel.util.StringBundler;
018    import com.liferay.portal.kernel.util.StringPool;
019    import com.liferay.portal.kernel.util.StringUtil;
020    
021    /**
022     * @author Shepherd Ching
023     * @author Jian Cao
024     * @author Laszlo Csontos
025     */
026    public class DB2Dialect extends org.hibernate.dialect.DB2Dialect {
027    
028            public DB2Dialect() {
029                    super();
030    
031                    registerKeyword("for");
032                    registerKeyword("optimize");
033            }
034    
035            @Override
036            public String getLimitString(String sql, int offset, int limit) {
037                    boolean hasOffset = false;
038    
039                    if ((offset > 0) || forceLimitUsage()) {
040                            hasOffset = true;
041                    }
042    
043                    StringBundler sb = null;
044    
045                    if (hasOffset) {
046                            sb = new StringBundler(11);
047                    }
048                    else {
049                            sb = new StringBundler(5);
050                    }
051    
052                    if (!hasOffset) {
053                            addQueryForLimitedRows(sb, sql, limit);
054                            addOptimizeForLimitedRows(sb, limit);
055    
056                            return sb.toString();
057                    }
058    
059                    // Outer query
060    
061                    sb.append("SELECT outerQuery.* FROM (");
062                    sb.append("SELECT ROW_NUMBER() OVER() AS rowNumber_, ");
063    
064                    // Inner query
065    
066                    sb.append("innerQuery.* FROM (");
067    
068                    addQueryForLimitedRows(sb, sql, limit);
069    
070                    sb.append(") AS innerQuery");
071    
072                    // Offset
073    
074                    sb.append(") AS outerQuery WHERE rowNumber_ > ");
075                    sb.append(offset);
076    
077                    addOptimizeForLimitedRows(sb, limit);
078    
079                    return sb.toString();
080            }
081    
082            @Override
083            public boolean supportsVariableLimit() {
084                    return _SUPPORTS_VARIABLE_LIMIT;
085            }
086    
087            protected void addOptimizeForLimitedRows(StringBundler sb, int limit) {
088                    sb.append(StringPool.SPACE);
089                    sb.append(
090                            StringUtil.replace(
091                                    _SQL_OPTIMIZE_FOR_LIMITED_ROWS, "[$LIMIT$]",
092                                    String.valueOf(limit)));
093            }
094    
095            protected void addQueryForLimitedRows(
096                    StringBundler sb, String sql, int limit) {
097    
098                    sb.append(sql);
099                    sb.append(StringPool.SPACE);
100                    sb.append(
101                            StringUtil.replace(
102                                    _SQL_FETCH_FIRST_LIMITED_ROWS_ONLY, "[$LIMIT$]",
103                                    String.valueOf(limit)));
104            }
105    
106            private static final String _SQL_FETCH_FIRST_LIMITED_ROWS_ONLY =
107                    "FETCH FIRST [$LIMIT$] ROWS ONLY";
108    
109            private static final String _SQL_OPTIMIZE_FOR_LIMITED_ROWS =
110                    "OPTIMIZE FOR [$LIMIT$] ROWS";
111    
112            private static final boolean _SUPPORTS_VARIABLE_LIMIT = false;
113    
114    }