541 words

javax.jdo.InstanceCallbacks - JDO interface

javax.jdo
Interface InstanceCallbacks

Superinterfaces:
ClearCallback, DeleteCallback, LoadCallback, StoreCallback
A PersistenceCapable class that provides callback methods for life cycle events implements this interface.

For JDO 2.0, InstanceCallbacks has been refactored to extend four other interfaces, without changing any of the methods or semantics. This allows fine-grained control over callbacks, for example to allow a class to implement the load callback without implementing any of the other callbacks. For backward compatibility with JDO 1.0, the InstanceCallbacks interface is preserved.

Classes which include non-persistent fields whose values depend on the values of persistent fields require callbacks on specific JDO instance life cycle events in order to correctly populate the values in these fields.

The callbacks might also be used if the persistent instances need to be put into the runtime infrastructure of the application. For example, a persistent instance might notify other instances on changes to state. The persistent instance might be in a list of managed instances. When the persistent instance is made hollow, it can no longer generate change events, and the persistent instance should be removed from the list of managed instances.

To implement this, the application programmer would implement jdoPostLoad to put itself into the list of managed instances, and implement jdoPreClear to remove itself from the list. With JDO 1.0, the domain class would be declared to implement InstanceCallbacks. With JDO 2.0, the domain class would be declared to implement javax.jdo.listener.LoadCallback and javax.jdo.listener.ClearCallback.

Note that JDO does not manage the state of non-persistent fields, and when a JDO instance transitions to hollow, JDO clears the persistent fields. It is the programmer's responsibility to clear non-persistent fields so that garbage collection of referred instances can occur.

Since:
JDO 1.0
Called after the values are loaded from the data store into this instance.
Called after the values are loaded from the data store into this instance.

This method is not modified by the enhancer.

Derived fields should be initialized in this method. The context in which this call is made does not allow access to other persistent JDO instances.

Since:
JDO 2.0
Called before the values in the instance are cleared.
Called before the values in the instance are cleared.

Transient fields should be cleared in this method. Associations between this instance and others in the runtime environment should be cleared.

This method is not modified by the enhancer.

Since:
JDO 2.0
Called before the instance is deleted.
Called before the instance is deleted. This method is called before the state transition to persistent-deleted or persistent-new-deleted. Access to field values within this call are valid. Access to field values after this call are disallowed.

This method is modified by the enhancer so that fields referenced can be used in the business logic of the method.

Since:
JDO 2.0
Called before the values are stored from this instance to the data store.
Called before the values are stored from this instance to the data store.

Data store fields that might have been affected by modified non-persistent fields should be updated in this method.

This method is modified by the enhancer so that changes to persistent fields will be reflected in the data store. The context in which this call is made allows access to the PersistenceManager and other persistent JDO instances.

Since:
JDO 2.0

This documentation page is derived (with some adjustments) from the JDO 2.2 API
and is available under the terms of the Apache License, v. 2.0.