/*****************************************************************
* 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.util;
import java.util.List;
import org.apache.cayenne.CayenneRuntimeException;
import org.apache.cayenne.FaultFailureException;
import org.apache.cayenne.Persistent;
import org.apache.cayenne.ValueHolder;
/**
* A ValueHolder implementation that holds a single Persistent object related to an object
* used to initialize PersistentObjectHolder. Value is resolved on first access.
*
* @since 1.2
*/
public class PersistentObjectHolder extends RelationshipFault implements ValueHolder {
protected boolean fault;
protected Object value;
// exists for the benefit of manual serialization schemes such as the one in Hessian.
@SuppressWarnings("unused")
private PersistentObjectHolder() {
fault = true;
}
public PersistentObjectHolder(Persistent relationshipOwner, String relationshipName) {
super(relationshipOwner, relationshipName);
fault = !isTransientParent();
}
/**
* Returns true if this holder is not resolved, meaning its object is not yet known.
*/
public boolean isFault() {
return fault;
}
public void invalidate() {
fault = true;
value = null;
}
/**
* Returns a value resolving it via a query on the first call to this method.
*/
public Object getValue() throws CayenneRuntimeException {
if (fault) {
resolve();
}
return value;
}
public Object getValueDirectly() throws CayenneRuntimeException {
return value;
}
/**
* Sets an object value, marking this ValueHolder as resolved.
*/
public synchronized Object setValue(Object value) throws CayenneRuntimeException {
if (fault) {
resolve();
}
Object oldValue = setValueDirectly(value);
if (oldValue != value && relationshipOwner.getObjectContext() != null) {
relationshipOwner.getObjectContext().propertyChanged(relationshipOwner, relationshipName, oldValue, value);
if (oldValue instanceof Persistent) {
Util.unsetReverse(relationshipOwner, relationshipName, (Persistent) oldValue);
}
if (value instanceof Persistent) {
Util.setReverse(relationshipOwner, relationshipName, (Persistent) value);
}
}
return oldValue;
}
public Object setValueDirectly(Object value) throws CayenneRuntimeException {
// must obtain the value from the local context
if (value instanceof Persistent) {
value = connect((Persistent) value);
}
Object oldValue = this.value;
this.value = value;
this.fault = false;
return oldValue;
}
/**
* Returns an object that should be stored as a value in this ValueHolder, ensuring
* that it is registered with the same context.
*/
protected Object connect(Persistent persistent) {
if (persistent == null) {
return null;
}
if (relationshipOwner.getObjectContext() != persistent.getObjectContext()) {
throw new CayenneRuntimeException(
"Cannot set object as destination of relationship "
+ relationshipName
+ " because it is in a different ObjectContext");
}
return persistent;
}
/**
* Reads an object from the database.
*/
protected synchronized void resolve() {
if (!fault) {
return;
}
// TODO: should build a HOLLOW object instead of running a query if relationship
// is required and thus expected to be not null.
List objects = resolveFromDB();
if (objects.size() == 0) {
this.value = null;
}
else if (objects.size() == 1) {
this.value = objects.get(0);
}
else {
throw new FaultFailureException(
"Expected either no objects or a single object, instead fault query resolved to "
+ objects.size()
+ " objects.");
}
fault = false;
}
}