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* 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
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****************************************************************/
package org.apache.cayenne.access.trans;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
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.
*/
public class OrderingTranslator extends QueryAssemblerHelper {
protected List<String> orderByColumnList = new ArrayList<String>();
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.
*
* @since 3.0
*/
@Override
protected void doAppendPart() throws IOException {
Query q = queryAssembler.getQuery();
// only select queries can have ordering...
if (q == null || !(q instanceof SelectQuery)) {
return;
}
Iterator<Ordering> it = ((SelectQuery) q).getOrderings().iterator();
Appendable mainBuffer = this.out;
try {
while (it.hasNext()) {
Ordering ord = it.next();
// reset buffer to collect SQL for the single column, that we'll be reusing
this.out = new StringBuilder();
if (ord.isCaseInsensitive()) {
out.append("UPPER(");
}
Expression exp = ord.getSortSpec();
if (exp.getType() == Expression.OBJ_PATH) {
appendObjPath(exp);
}
else if (exp.getType() == Expression.DB_PATH) {
appendDbPath(exp);
}
else {
throw new CayenneRuntimeException("Unsupported ordering expression: "
+ exp);
}
// Close UPPER() modifier
if (ord.isCaseInsensitive()) {
out.append(")");
}
String columnSQL = out.toString();
mainBuffer.append(columnSQL);
orderByColumnList.add(columnSQL);
// "ASC" is a noop, omit it from the query
if (!ord.isAscending()) {
mainBuffer.append(" DESC");
}
if (it.hasNext()) {
mainBuffer.append(", ");
}
}
}
finally {
this.out = mainBuffer;
}
}
/**
* 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<String> getOrderByColumnList() {
return orderByColumnList;
}
}