/*
* This library is part of OpenCms -
* the Open Source Content Management System
*
* Copyright (c) Alkacon Software GmbH (http://www.alkacon.com)
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* For further information about Alkacon Software, please see the
* company website: http://www.alkacon.com
*
* For further information about OpenCms, please see the
* project website: http://www.opencms.org
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package org.opencms.db;
/**
* Wrapper for {@link CmsSelectQuery} objects which adds SQL code for results paging.<p>
*
* The wrapper can either use the window function approach to paging or append a LIMIT/OFFSET clause.
*
* @see "http://troels.arvin.dk/db/rdbms/#select-limit-offset"
*
* @since 8.0.0
*/
public class CmsPagingQuery implements I_CmsQueryFragment {
/** Flag which indicates whether subqueries should be named. */
private boolean m_nameSubquery;
/** The current page. */
private int m_page;
/** The page size. */
private int m_pageSize;
/** The wrapped query. */
private CmsSelectQuery m_select;
/** If true, use window functions, else use a LIMIT/OFFSET clause. */
private boolean m_useWindowFunctions;
/**
* Creates a new instance.<p>
*
* @param select the wrapped query
*/
public CmsPagingQuery(CmsSelectQuery select) {
m_select = select;
}
/**
* Enables or disables the naming of subqueries.<p>
*
* @param nameSubquery if true, enables naming of subqueries
*/
public void setNameSubquery(boolean nameSubquery) {
m_nameSubquery = nameSubquery;
}
/**
* Sets both the page size and current page to use for the query.<p>
*
* @param pageSize the page size
* @param page the current page (counting starts at 1)
*/
public void setPaging(int pageSize, int page) {
m_pageSize = pageSize;
m_page = page;
}
/**
* Enables the use of window functions.<p>
*
* @param useWindowFunctions if true, enables window functions
*/
public void setUseWindowFunctions(boolean useWindowFunctions) {
m_useWindowFunctions = useWindowFunctions;
}
/**
* @see org.opencms.db.I_CmsQueryFragment#visit(org.opencms.db.CmsStatementBuilder)
*/
public void visit(CmsStatementBuilder builder) {
if (m_useWindowFunctions) {
I_CmsQueryFragment order = m_select.getOrdering();
assert order != null;
CmsCompositeQueryFragment rownumFragment = new CmsCompositeQueryFragment();
rownumFragment.add(new CmsSimpleQueryFragment("ROW_NUMBER() OVER (ORDER BY "));
rownumFragment.add(order);
rownumFragment.add(new CmsSimpleQueryFragment(") AS rownumber"));
m_select.addColumn(rownumFragment);
builder.add("SELECT * FROM ( ");
m_select.visit(builder);
int start = 1 + m_pageSize * (m_page - 1);
int end = start + m_pageSize - 1;
builder.add(")");
if (m_nameSubquery) {
builder.add(" AS rnsq ");
}
builder.add(" WHERE rownumber BETWEEN " + start + " AND " + end);
} else {
m_select.visit(builder);
int offset = (m_page - 1) * m_pageSize;
builder.add("\nLIMIT " + m_pageSize + " OFFSET " + offset);
}
}
}