oracle.toplink.essentials.queryframework

Class FetchGroup

java.lang.Object

oracle.toplink.essentials.queryframework.FetchGroup

All Implemented Interfaces:

Serializable

public class FetchGroup
extends Object
implements Serializable

Purpose: A fetch group is a performance enhancement that allows a group of attributes of an object to be loaded on demand, which means that the data for an attribute might not loaded from the underlying data source until an explicit access call for the attribute first occurs. It avoids the wasteful practice of loading up all data of the object?s attributes, in which the user is interested in only partial of them. A great deal of caution and careful system use case analysis should be use when using the fetch group feature, as the extra round-trip would well offset the gain from the deferred loading in many cases. TopLink fetch group support is twofold: the pre-defined fetch groups at the descriptor level; and dynamic (use case) fetch groups at the query level. TopLink fetch group support is only on CMP project. Every query can has at most one fetch group. There is an optional pre-defined default fetch group at the descriptor level. If set, and the query has no fetch group being set, the default fetch group would be used, unless query.setShouldUseDefaultFetchGroup(false) is also called. In the latter case, the full object will be fetched after the query execution.

Since:

TopLink 10.1.3.

Author:

King Wang

See Also:

FetchGroup, FetchGroupTracker, Serialized Form

Constructor Summary

Constructors

Constructor and Description
FetchGroup() Constructor.
FetchGroup(String name) Constructor with a group name.

Method Summary

Modifier and Type	Method and Description
void	addAttribute(String attrName) Add an attribute to the group
void	addAttributes(Set newAttributes) Add a set of attributes to the group
void	addFetchGroupAttribute(Expression attributeExpression) INTERNAL: Specify that only a subset of the class' attributes be fetched in this query.
Set	getAttributes() Return all attributes defined in the group
List	getFetchGroupAttributeExpressions() INTERNAL: Return the attibute expression list.
String	getName() Return the group name
boolean	hasFetchGroupAttributeExpressions() INTERNAL: Return if fetch group attributes.
boolean	isSupersetOf(FetchGroup anotherGroup) INTERNAL: Return true if this fetch group is a super-set of the passed in fetch group
void	removeAttribute(String attrName) Remove an attribute from the group
void	setFetchGroupAttributeExpressions(List fetchGroupAttributeExpressions) INTERNAL: Set the attibute expression list.
void	setName(String name) Set the group name

Methods inherited from class java.lang.Object

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

Constructor Detail

FetchGroup

public FetchGroup()

Constructor.

FetchGroup

public FetchGroup(String name)

Constructor with a group name.

Method Detail

getAttributes

public Set getAttributes()

Return all attributes defined in the group

addAttribute

public void addAttribute(String attrName)

Add an attribute to the group

addAttributes

public void addAttributes(Set newAttributes)

Add a set of attributes to the group

removeAttribute

public void removeAttribute(String attrName)

Remove an attribute from the group

getName

public String getName()

Return the group name

setName

public void setName(String name)

Set the group name

isSupersetOf

public boolean isSupersetOf(FetchGroup anotherGroup)

INTERNAL: Return true if this fetch group is a super-set of the passed in fetch group

getFetchGroupAttributeExpressions

public List getFetchGroupAttributeExpressions()

INTERNAL: Return the attibute expression list.

setFetchGroupAttributeExpressions

public void setFetchGroupAttributeExpressions(List fetchGroupAttributeExpressions)

INTERNAL: Set the attibute expression list.

hasFetchGroupAttributeExpressions

public boolean hasFetchGroupAttributeExpressions()

INTERNAL: Return if fetch group attributes.

addFetchGroupAttribute

public void addFetchGroupAttribute(Expression attributeExpression)

INTERNAL: Specify that only a subset of the class' attributes be fetched in this query.

This allows for the query to be optimized through selecting less data.

Partial objects will be returned from the query, where the unspecified attributes will be left in their default value. The primary key, and optimistic locking version (version or timestamp) if defined, will always be fetched. The partial object is cached and can be modified. An access through getter to an un-fetched attribute will trigger another SELECT to load the whole object.

Note: Modifying un-fetched attribute is not supported and exception would thrown.