org.hydrateframework.event
Interface ObjectAccessEventHandler

All Known Implementing Classes:

ObjectAccessEventHandler.EmptyAccessEventHandler, ObjectAccessEventHandler.LazyCollectionEventHandler, ObjectAccessEventHandler.LazyLoadAccessEventHandler, ObjectAccessEventHandler.WaitForPopulationEventHandler

public interface ObjectAccessEventHandler

This interface is used to defer control to the developer over events that occur when an object is being accessed.

Author:

david

Nested Class Summary

static class	ObjectAccessEventHandler.EmptyAccessEventHandler
static class	ObjectAccessEventHandler.LazyCollectionEventHandler
static class	ObjectAccessEventHandler.LazyLoadAccessEventHandler
static class	ObjectAccessEventHandler.WaitForPopulationEventHandler

Method Summary

boolean	attributeNotLoaded(HydrateObject object, java.lang.String attribute) This event method is called when an attempt is made to access an attribute of an object that has not been loaded.
boolean	collectionNotLoaded(HydrateObject object, java.lang.String attribute) This event method is called when an attempt is made to access a collection attribute of an object that has not been loaded.
java.util.Collection	getWeakCollection(HydrateObject obj, java.lang.String attr, java.lang.Class collClass) This method is needed to resolve the obscure, but tricky relationship between autoload references and lazy loading.

Method Detail

attributeNotLoaded

boolean attributeNotLoaded(HydrateObject object,
                           java.lang.String attribute)

This event method is called when an attempt is made to access an attribute of an object that has not been loaded. Implementors of this method have an opportunity to do something about the fact that the attribute was not populated such as setting it to a default value, reading it from a database or waiting for it to get populated by another thread

Parameters:

object - the object that had an attribute that was not loaded

attribute - the identifier corresponding to the attribute that was not set.

Returns:

true if the calling code should check to see if the attribute is not set and, if not call this method again. False if the calling code should check to see if the attribute is not set and throw a NotLoadedException if not.

collectionNotLoaded

boolean collectionNotLoaded(HydrateObject object,
                            java.lang.String attribute)

This event method is called when an attempt is made to access a collection attribute of an object that has not been loaded.

Parameters:

object - the object that had an attribute that was not loaded

attribute - the identifier corresponding to the collection attribute that was not set.

Returns:

true if the calling code should check to see if the attribute is not set and, if not call this method again. False if the calling code should check to see if the attribute is not set and throw a NotLoadedException if not.

See Also:

attributeNotLoaded(HydrateObject, String)

getWeakCollection

java.util.Collection getWeakCollection(HydrateObject obj,
                                       java.lang.String attr,
                                       java.lang.Class collClass)

This method is needed to resolve the obscure, but tricky relationship between autoload references and lazy loading. Our problem is that on loading objects we often implicitly fix up back references to unloaded collections. However, this gets in the way of the lazy loading of collections because either the collection will try and load when the back reference is created, or it will block subsequent implicit loading of the full collection afterwards. The solution is to permit weakly referenced collections that are not part of the class until explicity created but can keep track of these back references in the meantime. This method requests the creation (or resolution) of such a weakly referenced collection. These collections should always disappear as soon as the object they belong to is eligible for garbage collection

Parameters:

obj - the hydrate object that needs a collection. Don't even start thinking about getting this to work with non-Hydrate objects.

attr - the name of the attribute (must be the static reference from the interface)

collClass - the class of the collection that would be created if there is none available.

Returns:

this method should return null if it doesn't implement collectionNotLoaded i.e. doesn't concern itself with lazy loading of collections. If it does, it must return a collection that 'belongs' to the given object. In other words, subsequent calls to this method must return the same collection, but that collection must be eligible for garbage collection when the object reference goes out of scope.