/**
* Gets the ID of the last pulled train update.
*
* @return the ID or -1 if there aren't any stored IDs.
*/
public static long getLatestUpdateId() {
StorageStats stats = getStorageStats();
if (stats != null) {
return stats.getLatestUpdateId();
}
// TODO: will stats ever be null?
// TODO: We should store the latest ID instead of querying for it.
// That way we don't run into a situation where the data store gets cleared and we end up
// pulling 200 updates.
// Attempt to just pull the value out of the cache.
// We assume that the latest updates will always live here.
@SuppressWarnings("unchecked")
List<TrainUpdate> cachedUpdates = (List<TrainUpdate>) cache.get(CACHED_UPDATES_KEY);
if (cachedUpdates != null && !cachedUpdates.isEmpty()) {
log.info("Fetched cache with size of : " + cachedUpdates.size());
return cachedUpdates.get(cachedUpdates.size() - 1).getTwitterId();
}
// If no cached updates were found, we must query the datastore.
long sinceId = -1;
PersistenceManager pm = PMF.get().getPersistenceManager();
try {
Query query = pm.newQuery(TrainUpdate.class);
query.setOrdering("date DESC");
query.setRange(0, 1);
@SuppressWarnings("unchecked")
List<TrainUpdate> oldUpdates = (List<TrainUpdate>) query.execute();
if (oldUpdates.size() > 0) {
sinceId = oldUpdates.get(0).getTwitterId();
}
} finally {
pm.close();
}
return sinceId;
}
/**
* Adds new updates to storage.
*
* @param newUpdates
*/
public static void addUpdates(List<TrainUpdate> newUpdates) {
if (newUpdates.isEmpty()) {
return;
}
// Add the new updates to the list of cached results.
@SuppressWarnings("unchecked")
List<TrainUpdate> cachedUpdates = (List<TrainUpdate>) cache.get(CACHED_UPDATES_KEY);
if (cachedUpdates == null) {
cachedUpdates = new ArrayList<TrainUpdate>();
}
log.info("Fetched cache with size of : " + cachedUpdates.size());
cachedUpdates.addAll(newUpdates);
// Update the storage stats
StorageStats stats = getStorageStats();
stats.setLatestUpdateId(newUpdates.get(0).getTwitterId());
// Attempt to persist the updates to the data store.
PersistenceManager pm = PMF.get().getPersistenceManager();
try {
pm.makePersistentAll(cachedUpdates);
pm.makePersistent(stats);
cachedUpdates.clear();
log.info("Cache cleared");
} catch (DatastoreTimeoutException ex) {
log.info("Couldn't write to datastore. caching instead");
} finally {
// No matter what happens, store the new cached results.
cache.remove(CACHED_QUERIES_KEY);
cache.put(CACHED_UPDATES_KEY, cachedUpdates);
cache.put(STORAGE_STATS_KEY, stats);
log.info("Updated cache to size of : " + cachedUpdates.size());
pm.close();
}
}
