/******************************************************************************* | |
* Copyright (c) 1998, 2013 Oracle and/or its affiliates. All rights reserved. | |
* This program and the accompanying materials are made available under the | |
* terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0 | |
* which accompanies this distribution. | |
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html | |
* and the Eclipse Distribution License is available at | |
* http://www.eclipse.org/org/documents/edl-v10.php. | |
* | |
* Contributors: | |
* Oracle - initial API and implementation from Oracle TopLink | |
******************************************************************************/ | |
package org.eclipse.persistence.internal.indirection; | |
import org.eclipse.persistence.mappings.DatabaseMapping; | |
import org.eclipse.persistence.mappings.ForeignReferenceMapping; | |
import org.eclipse.persistence.queries.*; | |
import org.eclipse.persistence.descriptors.ClassDescriptor; | |
import org.eclipse.persistence.exceptions.*; | |
import org.eclipse.persistence.internal.sessions.AbstractRecord; | |
import org.eclipse.persistence.internal.sessions.AbstractSession; | |
import org.eclipse.persistence.internal.sessions.UnitOfWorkImpl; | |
/** | |
* QueryBasedValueHolder wraps a database-stored object and implements behavior | |
* to access it. The object is read from the database by invoking a | |
* user-specified query. | |
* | |
* @see ObjectLevelReadQuery | |
* @author Dorin Sandu | |
*/ | |
public class QueryBasedValueHolder extends DatabaseValueHolder { | |
/** | |
* Stores the query to be executed. | |
*/ | |
protected transient ReadQuery query; | |
protected transient Object sourceObject; | |
protected Integer refreshCascade; | |
protected QueryBasedValueHolder() { | |
} | |
/** | |
* Initialize the query-based value holder. | |
*/ | |
public QueryBasedValueHolder(ReadQuery query, AbstractRecord row, AbstractSession session) { | |
this(query, null, row, session); | |
} | |
/** | |
/** | |
* Store the uow identity so that it can be used to determine new | |
* transaction logic | |
*/ | |
/** | |
* Initialize the query-based value holder. | |
*/ | |
public QueryBasedValueHolder(ReadQuery query, Object sourceObject, AbstractRecord row, AbstractSession session) { | |
this.row = row; | |
this.session = session; | |
// Make sure not to put a ClientSession or IsolatedClientSession in | |
// the shared cache (indirectly). | |
// Skip this if unitOfWork, for we use session.isUnitOfWork() to | |
// implement | |
// isTransactionalValueholder(), saving us from needing a boolean | |
// instance variable. | |
// If unitOfWork this safety measure is deferred until merge time with | |
// releaseWrappedValuehHolder. | |
// Note that if isolated session & query will return itself, which is | |
// safe | |
// for if isolated it will not go in the shared cache. | |
if (!session.isUnitOfWork()) { | |
this.session = session.getRootSession(query); | |
} | |
this.query = query; | |
this.sourceObject = sourceObject; | |
} | |
/** | |
* INTERNAL: | |
* Returns the refresh cascade policy that was set on the query that was used to instantiate the valueholder | |
* a null value means that a non refresh query was used. | |
*/ | |
public Integer getRefreshCascadePolicy(){ | |
return this.refreshCascade; | |
} | |
/** | |
* Process against the UOW and attempt to load a local copy before going to the shared cache | |
* If null is returned then the calling UOW will instantiate as normal. | |
*/ | |
@Override | |
public Object getValue(UnitOfWorkImpl uow) { | |
if (this.query.isReadObjectQuery()){ | |
return this.query.getQueryMechanism().checkCacheForObject(this.query.getTranslationRow(), uow); | |
} | |
//not able to shortcircuit cache lookup to UOW return null; | |
return null; | |
} | |
/** | |
* Return the query. The query for a QueryBasedValueHolder is constructed | |
* dynamically based on the original query on the parent object and the | |
* mapping configuration. If modifying a query the developer must be careful | |
* not to change the results returned as that may cause the application to | |
* see incorrect results. | |
*/ | |
public ReadQuery getQuery() { | |
return query; | |
} | |
protected Object instantiate() throws DatabaseException { | |
return instantiate(this.session); | |
} | |
/** | |
* Instantiate the object by executing the query on the session. | |
*/ | |
protected Object instantiate(AbstractSession session) throws DatabaseException { | |
if (session == null) { | |
throw ValidationException.instantiatingValueholderWithNullSession(); | |
} | |
if (this.query.isObjectBuildingQuery() && ((ObjectBuildingQuery)this.query).shouldRefreshIdentityMapResult()){ | |
this.refreshCascade = ((ObjectBuildingQuery)this.query).getCascadePolicy(); | |
} | |
return session.executeQuery(getQuery(), getRow()); | |
} | |
/** | |
* Triggers UnitOfWork valueholders directly without triggering the wrapped | |
* valueholder (this). | |
* <p> | |
* When in transaction and/or for pessimistic locking the | |
* UnitOfWorkValueHolder needs to be triggered directly without triggering | |
* the wrapped valueholder. However only the wrapped valueholder knows how | |
* to trigger the indirection, i.e. it may be a batchValueHolder, and it | |
* stores all the info like the row and the query. Note: This method is not | |
* thread-safe. It must be used in a synchronized manner | |
*/ | |
public Object instantiateForUnitOfWorkValueHolder(UnitOfWorkValueHolder unitOfWorkValueHolder) { | |
return instantiate(unitOfWorkValueHolder.getUnitOfWork()); | |
} | |
/** | |
* INTERNAL: | |
* Run any extra code required after the valueholder instantiates | |
* For query based VH, we notify the cache that the valueholder has been triggered | |
*/ | |
public void postInstantiate(){ | |
DatabaseMapping mapping = query.getSourceMapping(); | |
if (mapping != null && mapping.isForeignReferenceMapping()){ | |
ClassDescriptor descriptor = mapping.getDescriptor(); | |
if (descriptor == null || descriptor.isAggregateDescriptor()){ | |
descriptor = session.getDescriptor(sourceObject); | |
} | |
if (descriptor != null){ | |
session.getIdentityMapAccessorInstance().getIdentityMap(descriptor).lazyRelationshipLoaded(sourceObject, this, (ForeignReferenceMapping)query.getSourceMapping()); | |
} | |
} | |
} | |
/** | |
* Releases a wrapped valueholder privately owned by a particular unit of | |
* work. | |
* <p> | |
* When unit of work clones are built directly from rows no object in the | |
* shared cache points to this valueholder, so it can store the unit of work | |
* as its session. However once that UnitOfWork commits and the valueholder | |
* is merged into the shared cache, the session needs to be reset to the | |
* root session, ie. the server session. | |
*/ | |
@Override | |
public void releaseWrappedValueHolder(AbstractSession targetSession) { | |
AbstractSession session = getSession(); | |
if ((session != null) && session.isUnitOfWork()) { | |
setSession(targetSession); | |
} | |
} | |
/** | |
* Reset all the fields that are not needed after instantiation. | |
*/ | |
protected void resetFields() { | |
super.resetFields(); | |
this.query = null; | |
} | |
/** | |
* Set the query. | |
*/ | |
protected void setQuery(ReadQuery theQuery) { | |
query = theQuery; | |
} | |
/** | |
* INTERNAL: Answers if this valueholder is a pessimistic locking one. Such | |
* valueholders are special in that they can be triggered multiple times by | |
* different UnitsOfWork. Each time a lock query will be issued. Hence even | |
* if instantiated it may have to be instantiated again, and once | |
* instantiated all fields can not be reset. | |
* <p> | |
* Since locks will be issued each time this valueholder is triggered, | |
* triggering this directly on the session in auto commit mode will generate | |
* an exception. This only UnitOfWorkValueHolder's wrapping this can trigger | |
* it. Note: This method is not thread-safe. It must be used in a | |
* synchronized manner | |
*/ | |
public boolean isPessimisticLockingValueHolder() { | |
// Get the easy checks out of the way first. | |
if ((this.query == null) || !this.query.isObjectLevelReadQuery()) { | |
return false; | |
} | |
ObjectLevelReadQuery query = (ObjectLevelReadQuery) this.query; | |
// Note even if the reference class is not locked, but the valueholder | |
// query | |
// has joined attributes, then this may count as a lock query. | |
// This means it is possible to trigger a valueholder to get an object | |
// which | |
// is not to be pess. locked and get an exception for triggering it on | |
// the | |
// session outside a transaction. | |
return query.isLockQuery(this.session); | |
} | |
public void setSourceObject(Object sourceObject) { | |
this.sourceObject = sourceObject; | |
} | |
} |