/*****************************************************************
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
****************************************************************/
package org.apache.cayenne.access.trans;
import java.util.ArrayList;
import java.util.List;
import org.apache.cayenne.CayenneRuntimeException;
import org.apache.cayenne.exp.Expression;
import org.apache.cayenne.query.Ordering;
import org.apache.cayenne.query.Query;
import org.apache.cayenne.query.SelectQuery;
/**
* Translates query ordering to SQL.
*
* @author Andrus Adamchik
* @author Craig Miskell
*/
public class OrderingTranslator extends QueryAssemblerHelper {
protected List orderByColumnList = new ArrayList();
public OrderingTranslator(QueryAssembler queryAssembler) {
super(queryAssembler);
}
/** Translates query Ordering list to SQL ORDER BY clause.
* Ordering list is obtained from <code>queryAssembler</code>'s query object.
* In a process of building of ORDER BY clause, <code>queryAssembler</code>
* is notified when a join needs to be added. */
public String doTranslation() {
Query q = queryAssembler.getQuery();
// only select queries can have ordering...
if (q == null || !(q instanceof SelectQuery))
return null;
StringBuffer buf = new StringBuffer();
List list = ((SelectQuery) q).getOrderings();
int len = list.size();
for (int i = 0; i < len; i++) {
if (i > 0)
buf.append(", ");
StringBuffer ordComp = new StringBuffer();
Ordering ord = (Ordering) list.get(i);
//UPPER is (I think) part of the SQL99 standard, and I'm not convinced it's universally available
// - should the syntax used here be defined by the Db specific adaptor perhaps, or at least
// possibly specified by the db adaptor (a DB specific OrderingTranslator hook)?
if (ord.isCaseInsensitive()) {
ordComp.append("UPPER(");
}
Expression exp = ord.getSortSpec();
if (exp.getType() == Expression.OBJ_PATH) {
appendObjPath(ordComp, exp);
} else if (exp.getType() == Expression.DB_PATH) {
appendDbPath(ordComp, exp);
} else {
throw new CayenneRuntimeException(
"Unsupported ordering expression: " + exp);
}
//Close UPPER() modifier
if (ord.isCaseInsensitive()) {
ordComp.append(")");
}
orderByColumnList.add(ordComp.toString());
buf.append(ordComp.toString());
// "ASC" is a noop, omit it from the query
if (!ord.isAscending()) {
buf.append(" DESC");
}
}
return buf.length() > 0 ? buf.toString() : null;
}
/**
* Returns the column expressions (not Expressions) used in
* the order by clause. E.g., in the case of an case-insensitive
* order by, an element of the list would be
* <code>UPPER(<column reference>)</code>
*/
public List getOrderByColumnList() {
return orderByColumnList;
}
}