Object Lifecycle

During the persistence process, an object goes through lifecycle changes. Below we demonstrate the primary object lifecycle changes for JDO

JDO has a very high degree of flexibility and so can be configured to operate in different modes. The mode most consistent with JPA is shown below (this has the PMF property DetachAllOnCommit set to true)

So a newly created object is transient . You then persist it and it becomes persistent . You then commit the transaction and it is detached for use elsewhere in the application. You then attach any changes back to persistence and it becomes persistent again. Finally when you delete the object from persistence and commit that transaction it is in transient state.

An alternative JDO lifecycle occurs when you have DetachAllOnCommit as false. Now at commit the object moves into hollow state (still has its identity, but its field values are optionally unloaded).

With JDO there are actually some additional lifecycle states, notably when an object has a field changed, becoming dirty , so you get an object in "persistent-dirty", "detached-dirty" states for example. The average user doesn't need to know about these so we don't cover them here. To inspect the lifecycle state of an object, simply call


Helper Methods

In addition to the JDOHelper method above, JDO provides a series of other helper methods for lifecycle operations. These are documented on the Apache JDO site.

Further to this DataNucleus provides yet more helper methods

String[] fieldNames = NucleusJDOHelper.getDirtyFields(pc, pm);
String[] fieldNames = NucleusJDOHelper.getLoadedFields(pc, pm);

These methods returns the names of the dirty/loaded fields in the supplied object. The pm argument is only required if the object is detached

Boolean dirty = NucleusJDOHelper.isDirty(pc, "fieldName", pm);
Boolean loaded = NucleusJDOHelper.isLoaded(pc, "fieldName", pm);

These methods returns whether the specified field in the supplied object is dirty/loaded. The pm argument is only required if the object is detached