net.sf.mmm.util.bean.base.link

Class IdLink<E extends EntityBean>

java.lang.Object

net.sf.mmm.util.bean.base.link.AbstractLink<E>

net.sf.mmm.util.bean.base.link.IdLink<E>

Type Parameters:

E - the generic type of the linked EntityBean.

All Implemented Interfaces:

Link<E>

public class IdLink<E extends EntityBean>
extends AbstractLink<E>

This is an implementation of Link that initially only carries the Id of an entity and allows lazy loading on the first call of getTarget() via an externally given resolver function. This approach is easier, less invasive and more lightweight as using proxy objects for entities.

Since:

8.0.0

Author:

hohwille

Field Summary

Fields

Modifier and Type	Field and Description
private E	entity
private Id<E>	id
private Function<Id<E>,E>	resolver

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	IdLink() The constructor (for serialization and strange frameworks).
protected	IdLink(Id<E> id, Function<Id<E>,E> resolver) The constructor.

Method Summary

Modifier and Type	Method and Description
Id<E>	getId()
E	getTarget() This method resolves the linked EntityBean. ATTENTION: An Link can be evaluated lazily.
boolean	isResolved()
private E	resolve()
static <E extends EntityBean> IdLink<E>	valueOf(Id<E> id, Function<Id<E>,E> resolver)

Methods inherited from class net.sf.mmm.util.bean.base.link.AbstractLink

equals, hashCode, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

id

private final Id<E extends EntityBean> id

resolver

private transient Function<Id<E extends EntityBean>,E extends EntityBean> resolver

entity

private E extends EntityBean entity

Constructor Detail

IdLink

protected IdLink()

The constructor (for serialization and strange frameworks).

IdLink

protected IdLink(Id<E> id,
                 Function<Id<E>,E> resolver)

The constructor.

Parameters:

id - - see getId().

resolver - the Function to resolve the link target (the entity).

Method Detail

getId

public Id<E> getId()

Returns:

the unique identifier of the linked bean. When creating new Beans a link may hold a transient EntityBean as target that has no ID assigned, yet. In such case this method will return null.

isResolved

public boolean isResolved()

Returns:

true if the link target is already resolved, false otherwise (if Link.getTarget() may trigger lazy loading and could also fail if called without an open transaction).

getTarget

public E getTarget()

Description copied from interface: Link

This method resolves the linked EntityBean.
ATTENTION:
An Link can be evaluated lazily. In such case the first call of this method will resolve the linked EntityBean from the database. That can be a relatively expensive operation and requires an open transaction. Use Link.isResolved() to distinguish and prevent undesired link resolving.
Further, after serialization (e.g. mapping to JSON and back) maybe only the ID was transferred and this link can not be resolved. In that case this method may return null. Please note that id and target can not both be null. In case a link property is empty it will contain null instead of an empty Link so you can always properly distinguish the scenarios.

Returns:

the link target or null if the link can not be resolved.

resolve

private E resolve()

Returns:

valueOf

public static <E extends EntityBean> IdLink<E> valueOf(Id<E> id,
                                                       Function<Id<E>,E> resolver)

Type Parameters:

E - the generic type of the linked EntityBean.

Parameters:

id - - see getId().

resolver - the Function to resolve the Id.

Returns:

the IdLink instance.