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* Licensed to the Apache Software Foundation (ASF) under one
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* 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.List;
import org.apache.cayenne.map.DbEntity;
import org.apache.cayenne.map.DbJoin;
import org.apache.cayenne.map.DbRelationship;
import org.apache.cayenne.map.JoinType;
/**
* Encapsulates join reuse/split logic used in SelectQuery processing. All expression
* path's that exist in the query (in the qualifier, etc.) are processed to produce a
* combined join tree.
*
* @since 3.0
*/
public class JoinStack {
protected JoinTreeNode rootNode;
protected JoinTreeNode topNode;
private int aliasCounter;
protected JoinStack() {
this.rootNode = new JoinTreeNode(this);
this.rootNode.setTargetTableAlias(newAlias());
resetStack();
}
String getCurrentAlias() {
return topNode.getTargetTableAlias();
}
/**
* Returns the number of configured joins.
*/
protected int size() {
// do not count root as a join
return rootNode.size() - 1;
}
void appendRoot(Appendable out, DbEntity rootEntity) throws IOException {
out.append(rootEntity.getFullyQualifiedName());
out.append(' ').append(rootNode.getTargetTableAlias());
}
/**
* Appends all configured joins to the provided output object.
*/
protected void appendJoins(Appendable out) throws IOException {
// skip root, recursively append its children
for (JoinTreeNode child : rootNode.getChildren()) {
appendJoinSubtree(out, child);
}
}
protected void appendJoinSubtree(Appendable out, JoinTreeNode node) throws IOException {
DbRelationship relationship = node.getRelationship();
DbEntity targetEntity = (DbEntity) relationship.getTargetEntity();
String srcAlias = node.getSourceTableAlias();
String targetAlias = node.getTargetTableAlias();
switch (node.getJoinType()) {
case INNER:
out.append(" JOIN");
break;
case LEFT_OUTER:
out.append(" LEFT JOIN");
break;
default:
throw new IllegalArgumentException("Unsupported join type: "
+ node.getJoinType());
}
out.append(' ').append(targetEntity.getFullyQualifiedName()).append(' ').append(
targetAlias).append(" ON (");
List<DbJoin> joins = relationship.getJoins();
int len = joins.size();
for (int i = 0; i < len; i++) {
DbJoin join = joins.get(i);
if (i > 0) {
out.append(" AND ");
}
out
.append(srcAlias)
.append('.')
.append(join.getSourceName())
.append(" = ")
.append(targetAlias)
.append('.')
.append(join.getTargetName());
}
out.append(')');
for (JoinTreeNode child : node.getChildren()) {
appendJoinSubtree(out, child);
}
}
/**
* Append join information to the qualifier - the part after "WHERE".
*/
protected void appendQualifier(Appendable out, boolean firstQualifyerElement)
throws IOException {
// nothing as standard join is performed before "WHERE"
}
/**
* Pops the stack all the way to the root node.
*/
void resetStack() {
topNode = rootNode;
}
/**
* Finds or creates a JoinTreeNode for the given arguments and sets it as the next
* current join.
*/
void pushJoin(DbRelationship relationship, JoinType joinType, String alias) {
topNode = topNode.findOrCreateChild(relationship, joinType, alias);
}
protected String newAlias() {
return "t" + aliasCounter++;
}
}