Upgrade the version of Blackberry persistent store class

When upgrading the version of Blackberry persistent store, like adding or removing a instance member in the persistent class, the saved persistent data will be automatically deleted by system.
To handle the version upgrading while storing the data in a single version instead of multiple versions of persistent classes, the application needs to keep the code of all older versions of persistent store in order to load the older data, and also upgrade the old version of data to latest version.

The logic are as follows:
VersionKeyArray =
{
OlderVersionKey1;
OlderVersionKey2;
LatestVersionKey3;
}

CurrentVersionKey = VersionJeyArray.LatestVersionKey3;
while (currentVersionKey != NULL)
{
get stored persistent object;
if (persistent object != NULL )
{
if ( is not the latest version )
{
read the older version of persistent data
Convert to the new version, this may involves crossing multiple versions
persist the new version of data
delete the older version of data
break;
}
}
go to the next older version key
}

//when the code gets here, we know we have the latest version of data
process the load persistent data if it is not null