The various lifecycle states supported by JPOX are shown below.
| Name | Description |
|---|
| Transient | Any object created by the developer that do are not persisted. These don't have a JDO identity. |
| Persistent New | Any object that is newly persisted in the current transaction. A JDO identity has been assigned to these objects. |
| Persistent Dirty | Any persistent object that has been changed in the current transaction. |
| Hollow | Any persistent object that represents data in the datastore, but whose values are not in the instance. |
| Persistent Clean | Any persistent object that represents data in the datastore, and whose values have not been changed in the current transaction. |
| Persistent Deleted | Any persistent object that represents data in the datastore, and that has been deleted in the current transaction. |
| Persistent New Deleted | Any object that have been newly made persistent and then deleted in the same current transaction. |
| Persistent Non transactional | Any persistent object that represents data in the datastore, whose values are loaded but not transactionally consistent. |
| Transient Clean | Any transient object that represents a transactional instance whose values have not been changed in the current transaction. |
| Transient Dirty | Any transient object that represents a transactional instance whose values have been changed in the current transaction. |
| Detached Clean | Any detached object that represents a persistent instance whose values have not been changed since detaching. |
| Detached Dirty | Any detached object that represents a persistent instance whose values have been changed since detaching. |
JDO provides a class JDOHelper that allows you to interrogate the object state. Unfortunately to get
the overall object state you would have to call up to 6 methods on JDOHelper. JPOX extends JDOHelper to provide
a convenience method
JPOX 1.1.4 or later
String state = org.jpox.JPOXHelper.getObjectState(obj);
JPOX 1.2 or later
String state = org.jpox.jdo.JPOXJDOHelper.getObjectState(obj);
The most basic thing you can do with JDO is persist an object. The following code is an example of how you can do this
Transaction tx=pm.currentTransaction();
try
{
tx.begin();
Product product=new Product("Sony Discman","A standard discman from Sony",49.99);
pm.makePersistent(product);
tx.commit();
}
finally
{
if (tx.isActive())
{
tx.rollback();
}
}
The Product object progresses from Transient (initial, unpersisted state), through to Persistent New, and then finally to Hollow when it reaches the data store (after the "commit"). If the persist failed, it would "rollback" and hence end up in the same state as when it started. The following diagram shows this graphically
When you have persisted objects you need to update them. The following code is an example of how you can do this
Transaction tx=pm.currentTransaction();
try
{
tx.begin();
String product_name=product.getName();
...
product.setPrice(75.0);
tx.commit();
}
finally
{
if (tx.isActive())
{
tx.rollback();
}
}
The Product object starts off in Hollow state and progresses to Persistent Clean when the user requires to read from it. It then migrates to Persistent Dirty when the price is updated. Finally it returns to Hollow when the user commits/rolls back the transaction. The following diagram shows this graphically
When you no longer need an object persisted, you can delete it. The following code is an example of how you can do this
Transaction tx=pm.currentTransaction();
try
{
tx.begin();
String product_name=product.getName();
...
pm.deletePersistent(product);
tx.commit();
}
finally
{
if (tx.isActive())
{
tx.rollback();
}
}
The Product object starts off in Hollow state and progresses to Persistent Clean when the user requires to read from it. It then migrates to Persistent Deleted when the deletePersistent() called. Finally it either progresses to Transient when commit is called, or returns to Hollow if it is rolled back. The following diagram shows this graphically
