Module org.eclipse.persistence.core

Package org.eclipse.persistence.internal.indirection

Class BatchValueHolder<T>

java.lang.Object

org.eclipse.persistence.internal.indirection.DatabaseValueHolder<T>

org.eclipse.persistence.internal.indirection.QueryBasedValueHolder<T>

org.eclipse.persistence.internal.indirection.BatchValueHolder<T>

All Implemented Interfaces:

Serializable, Cloneable, ValueHolderInterface<T>, WeavedAttributeValueHolderInterface<T>

public class BatchValueHolder<T>
extends QueryBasedValueHolder<T>

BatchValueHolder is used by the mappings that use indirection when using query optimization (batch reading). This value holder is different from QueryBasedValueHolder in that its value must be extracted from one of the results return by the query, not the entire result. The query is also shared by all other value holders within the batch and it must be ensured that the query is only executed once. Concurrency must also be maintained across all of the value holders in the batch.

See Also:

• Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
protected ForeignReferenceMapping	mapping
protected ObjectLevelReadQuery	originalQuery
protected CacheKey	parentCacheKey

Fields inherited from class org.eclipse.persistence.internal.indirection.QueryBasedValueHolder

query, refreshCascade, sourceObject

Fields inherited from class org.eclipse.persistence.internal.indirection.DatabaseValueHolder

isCoordinatedWithProperty, isInstantiated, row, session, value

Fields inherited from interface org.eclipse.persistence.indirection.ValueHolderInterface

shouldToStringInstantiate

Constructor Summary

Constructors

Constructor	Description
BatchValueHolder(ReadQuery query, AbstractRecord row, ForeignReferenceMapping mapping, ObjectLevelReadQuery originalQuery, CacheKey parentCacheKey)	Initialize the query-based value holder.

Method Summary

Modifier and Type	Method	Description
protected ForeignReferenceMapping	getMapping()
protected T	instantiate(AbstractSession session)	Instantiate the object by having the mapping extract its value from the query.
T	instantiateForUnitOfWorkValueHolder(UnitOfWorkValueHolder<T> unitOfWorkValueHolder)	Triggers UnitOfWork valueholders directly without triggering the wrapped valueholder (this).
boolean	isEasilyInstantiated()	INTERNAL: Answers if this valueholder is easy to instantiate.
protected void	resetFields()	Reset all the fields that are not needed after instantiation.
protected void	setMapping(ForeignReferenceMapping mapping)

Methods inherited from class org.eclipse.persistence.internal.indirection.QueryBasedValueHolder

getQuery, getRefreshCascadePolicy, getValue, instantiate, isPessimisticLockingValueHolder, postInstantiate, releaseWrappedValueHolder, setQuery, setRefreshCascadePolicy, setSourceObject

Methods inherited from class org.eclipse.persistence.internal.indirection.DatabaseValueHolder

clone, getRow, getSession, getValue, getWrappedValueHolder, isCoordinatedWithProperty, isInstantiated, isNewlyWeavedValueHolder, isSerializedRemoteUnitOfWorkValueHolder, isTransactionalValueHolder, privilegedSetValue, setInstantiated, setIsCoordinatedWithProperty, setIsNewlyWeavedValueHolder, setRow, setSession, setUninstantiated, setValue, shouldAllowInstantiationDeferral, toString

Methods inherited from class java.lang.Object

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

Field Details

mapping

protected transient ForeignReferenceMapping mapping

originalQuery

protected transient ObjectLevelReadQuery originalQuery

parentCacheKey

protected transient CacheKey parentCacheKey

Constructor Details

BatchValueHolder

public BatchValueHolder(ReadQuery query,
 AbstractRecord row,
 ForeignReferenceMapping mapping,
 ObjectLevelReadQuery originalQuery,
 CacheKey parentCacheKey)

Initialize the query-based value holder.

Parameters:

query - The query that returns the object when executed.

row - The row representation of the object.

mapping - The mapping that is uses batch reading.

Method Details

getMapping

protected ForeignReferenceMapping getMapping()

instantiate

protected T instantiate(AbstractSession session)
                 throws EclipseLinkException

Instantiate the object by having the mapping extract its value from the query. Concurrency must be maintained across all of the value holders, since they all share the same query, the extractResultFromBatchQuery method must be synchronized.

Overrides:

instantiate in class QueryBasedValueHolder<T>

Throws:

EclipseLinkException

instantiateForUnitOfWorkValueHolder

public T instantiateForUnitOfWorkValueHolder(UnitOfWorkValueHolder<T> unitOfWorkValueHolder)

Triggers UnitOfWork valueholders directly without triggering the wrapped valueholder (this).

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. The batch value holder must use a batch query relative to the unit of work, as the batch is local to the unit of work.

Overrides:

instantiateForUnitOfWorkValueHolder in class QueryBasedValueHolder<T>

isEasilyInstantiated

public boolean isEasilyInstantiated()

INTERNAL: Answers if this valueholder is easy to instantiate.

Overrides:

isEasilyInstantiated in class DatabaseValueHolder<T>

Returns:

true if getValue() won't trigger a database read.

resetFields

protected void resetFields()

Reset all the fields that are not needed after instantiation.

Overrides:

resetFields in class QueryBasedValueHolder<T>

setMapping

protected void setMapping(ForeignReferenceMapping mapping)