org.exolab.castor.persist

Class QueryResults

java.lang.Object

org.exolab.castor.persist.QueryResults

public final class QueryResults
extends Object

The result of a query in the context of a transaction. A query is executed against the cache engine in the context of a transaction. The result of a query is this object that can be used to obtain the next object in the query.

Version:

$Revision: 7951 $ $Date: 2006-04-22 11:05:30 -0600 (Sat, 22 Apr 2006) $

Author:

Assaf Arkin

Constructor Summary

Constructors

Constructor and Description
QueryResults(TransactionContext tx, LockEngine engine, PersistenceQuery query, AccessMode accessMode, Database db)

Method Summary

Methods

Modifier and Type	Method and Description
boolean	absolute(int row)
void	close() Close the query and release all resources held by the query.
Object	fetch() Loads the specified object with the identity.
PersistenceQuery	getQuery() Returns the associated query.
Class	getResultType() Returns the type of object returned by this query.
TransactionContext	getTransaction() Returns the transaction context in which this query was opened.
Object	nextIdentity() Returns the identity of the next object to be returned.
int	size()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

QueryResults

public QueryResults(TransactionContext tx,
            LockEngine engine,
            PersistenceQuery query,
            AccessMode accessMode,
            Database db)

Method Detail

getTransaction

public TransactionContext getTransaction()

Returns the transaction context in which this query was opened. The transaction may be closed.

Returns:

The query's transaction context

getQuery

public PersistenceQuery getQuery()

Returns the associated query.

Returns:

The query

getResultType

public Class getResultType()

Returns the type of object returned by this query.

Returns:

The type of object returned by this query

nextIdentity

public Object nextIdentity()
                    throws PersistenceException

Returns the identity of the next object to be returned. Calling this method multiple time will skip objects. When the result set has been exhuasted, this method will return null.

Returns:

The identity of the next object

Throws:

PersistenceException - An error reported by the persistence engine

TransactionNotInProgressException - The transaction has been closed

fetch

public Object fetch()
             throws PersistenceException

Loads the specified object with the identity. The identity must have been retrieved with a call to nextIdentity().

If the object is locked by another transaction this method will block until the lock is released, or a timeout occured. If a timeout occurs or the object has been deleted by the other transaction, this method will report an. The query may proceed to the next identity.

If the object has been deleted in this transaction, this method will report an. However, the caller may iterate to and obtain the next object.

This method is equivalent to TransactionContext.fetch(org.exolab.castor.persist.ClassMolder, org.exolab.castor.persist.spi.Identity, org.exolab.castor.mapping.AccessMode) with a know cache engine, identity and lock and acts on the query results rather than issuing a new query to load the object.

Returns:

The loaded object

Throws:

PersistenceException - An error reported by the persistence engine. The object was not found in persistent storage. The transaction has been closed. Could not acquire a lock on the object.

close

public void close()

Close the query and release all resources held by the query.

absolute

public boolean absolute(int row)
                 throws PersistenceException

Throws:

PersistenceException

size

public int size()
         throws PersistenceException

Throws:

PersistenceException