Package org.eclipse.persistence.internal.indirection

Class QueryBasedValueHolder

java.lang.Object

org.eclipse.persistence.internal.indirection.DatabaseValueHolder

org.eclipse.persistence.internal.indirection.QueryBasedValueHolder

All Implemented Interfaces:

Serializable, Cloneable, ValueHolderInterface, WeavedAttributeValueHolderInterface

Direct Known Subclasses:

BatchValueHolder, EISOneToManyQueryBasedValueHolder

public class QueryBasedValueHolder
extends DatabaseValueHolder

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.

Author:

Dorin Sandu

See Also:

ObjectLevelReadQuery, Serialized Form

Field Summary

Fields

Modifier and Type	Field	Description
protected ReadQuery	query	Stores the query to be executed.
protected Integer	refreshCascade
protected Object	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

Modifier	Constructor	Description
protected	QueryBasedValueHolder()
	QueryBasedValueHolder(ReadQuery query, Object sourceObject, AbstractRecord row, AbstractSession session)	Initialize the query-based value holder.
	QueryBasedValueHolder(ReadQuery query, AbstractRecord row, AbstractSession session)	Initialize the query-based value holder.

Method Summary

Modifier and Type	Method	Description
ReadQuery	getQuery()	Return the query.
Integer	getRefreshCascadePolicy()	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.
Object	getValue(UnitOfWorkImpl uow)	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.
protected Object	instantiate()	Instantiate the object.
protected Object	instantiate(AbstractSession session)	Instantiate the object by executing the query on the session.
Object	instantiateForUnitOfWorkValueHolder(UnitOfWorkValueHolder unitOfWorkValueHolder)	Triggers UnitOfWork valueholders directly without triggering the wrapped valueholder (this).
boolean	isPessimisticLockingValueHolder()	INTERNAL: Answers if this valueholder is a pessimistic locking one.
void	postInstantiate()	INTERNAL: Run any extra code required after the valueholder instantiates For query based VH, we notify the cache that the valueholder has been triggered
void	releaseWrappedValueHolder(AbstractSession targetSession)	Releases a wrapped valueholder privately owned by a particular unit of work.
protected void	resetFields()	Reset all the fields that are not needed after instantiation.
protected void	setQuery(ReadQuery theQuery)	Set the query.
void	setRefreshCascadePolicy(Integer refreshCascadePolicy)	INTERNAL:
void	setSourceObject(Object sourceObject)

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

clone, getRow, getSession, getValue, getWrappedValueHolder, isCoordinatedWithProperty, isEasilyInstantiated, 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 Detail

query

protected transient ReadQuery query

Stores the query to be executed.

sourceObject

protected transient Object sourceObject

refreshCascade

protected Integer refreshCascade

Constructor Detail

QueryBasedValueHolder

protected QueryBasedValueHolder()

QueryBasedValueHolder

public QueryBasedValueHolder(ReadQuery query,
                             AbstractRecord row,
                             AbstractSession session)

Initialize the query-based value holder.

QueryBasedValueHolder

public QueryBasedValueHolder(ReadQuery query,
                             Object sourceObject,
                             AbstractRecord row,
                             AbstractSession session)

Initialize the query-based value holder.

Method Detail

getRefreshCascadePolicy

public Integer getRefreshCascadePolicy()

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.

getValue

public Object getValue(UnitOfWorkImpl uow)

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.

Overrides:

getValue in class DatabaseValueHolder

getQuery

public ReadQuery getQuery()

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.

instantiate

protected Object instantiate()
                      throws DatabaseException

Description copied from class: DatabaseValueHolder

Instantiate the object.

Specified by:

instantiate in class DatabaseValueHolder

Throws:

DatabaseException

instantiate

protected Object instantiate(AbstractSession session)
                      throws DatabaseException

Instantiate the object by executing the query on the session.

Throws:

DatabaseException

instantiateForUnitOfWorkValueHolder

public Object instantiateForUnitOfWorkValueHolder(UnitOfWorkValueHolder 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

Specified by:

instantiateForUnitOfWorkValueHolder in class DatabaseValueHolder

postInstantiate

public void postInstantiate()

INTERNAL: Run any extra code required after the valueholder instantiates For query based VH, we notify the cache that the valueholder has been triggered

Overrides:

postInstantiate in class DatabaseValueHolder

See Also:

QueryBasedValueHolder

releaseWrappedValueHolder

public void releaseWrappedValueHolder(AbstractSession targetSession)

Releases a wrapped valueholder privately owned by a particular unit of work.

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.

Overrides:

releaseWrappedValueHolder in class DatabaseValueHolder

resetFields

protected void resetFields()

Reset all the fields that are not needed after instantiation.

Overrides:

resetFields in class DatabaseValueHolder

setQuery

protected void setQuery(ReadQuery theQuery)

Set the query.

isPessimisticLockingValueHolder

public boolean isPessimisticLockingValueHolder()

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.

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

Specified by:

isPessimisticLockingValueHolder in class DatabaseValueHolder

setSourceObject

public void setSourceObject(Object sourceObject)

setRefreshCascadePolicy

public void setRefreshCascadePolicy(Integer refreshCascadePolicy)

INTERNAL:

Parameters:

refreshCascadePolicy -