org.apache.openjpa.persistence.criteria.CriteriaExpressionVisitor Maven / Gradle / Ivy
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* 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
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* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
package org.apache.openjpa.persistence.criteria;
import java.util.HashSet;
import java.util.Set;
/**
* A visitor for Criteria Expression nodes.
*
* @author Pinaki Poddar
* @since 2.0.0
*
*/
public interface CriteriaExpressionVisitor {
// Enumerates order of traversal of nodes
public static enum TraversalStyle {
INFIX, // operand1 operator operand2 e.g. a + b
POSTFIX, // operand1 operand2 operator e.g. a b +
PREFIX, // operator operand1 operand2 e.g. + a b
FUNCTION // operator(operand1, operand2) e.g. f(a,b)
}
/**
* Enter the given node.
*/
void enter(CriteriaExpression node);
/**
* Exit the given node.
*/
void exit(CriteriaExpression node);
/**
* Affirms if this node has been visited.
*/
boolean isVisited(CriteriaExpression node);
/**
* Get the traversal style of the children of the given node.
*/
TraversalStyle getTraversalStyle(CriteriaExpression node);
/**
* An abstract implementation that can detect cycles during traversal.
*
*/
public static abstract class AbstractVisitor implements CriteriaExpressionVisitor {
protected final Set _visited = new HashSet<>();
/**
* Remembers the node being visited.
*/
@Override
public void exit(CriteriaExpression node) {
_visited.add(node);
}
/**
* Affirms if this node has been visited before.
*/
@Override
public boolean isVisited(CriteriaExpression node) {
return _visited.contains(node);
}
/**
* Returns PREFIX as the default traversal style.
*/
@Override
public TraversalStyle getTraversalStyle(CriteriaExpression node) {
return TraversalStyle.PREFIX;
}
}
/**
* A visitor to register Parameter expression of a query.
*
*/
public static class ParameterVisitor extends AbstractVisitor {
private final CriteriaQueryImpl query;
public ParameterVisitor(CriteriaQueryImpl q) {
query = q;
}
@Override
public void enter(CriteriaExpression expr) {
if (expr instanceof ParameterExpressionImpl) {
query.registerParameter((ParameterExpressionImpl)expr);
}
}
}
}