I spent few hours to find nice example for
"com.google.appengine.api.datastore.Cursor".
Requirement is simple, for each gwt rpc call return one record along
with encoded cursor (similar to oracle pl/sql cursor).
On subsequent calls, decode cursor and reposition preparedquery to
fetch next record.
here is the sample code.
=============================================================
public static Question getNextQuestion(String encodedCursor,
String tableName) {
DatastoreService ds =
DatastoreServiceFactory.getDatastoreService();
Query query = new Query(tableName);
PreparedQuery pq = ds.prepare(query);
// FetchOptions fetchOptions = Builder.withDefaults();
FetchOptions fetchOptions = FetchOptions.Builder.withLimit(1);
QueryResultList<Entity> nextBatch = null;
String encodedCursortmp = null;
Cursor cursor = null;
if (encodedCursor == null) {
nextBatch = pq.asQueryResultList(fetchOptions);
cursor = nextBatch.getCursor();
encodedCursortmp = cursor.toWebSafeString();
} else {
Cursor decodedCursor =
Cursor.fromWebSafeString(encodedCursor);
nextBatch = pq.asQueryResultList(fetchOptions
.startCursor(decodedCursor));
// pq.asQueryResultList(fetchOptions).getCursor();
cursor = nextBatch.getCursor();
encodedCursortmp = cursor.toWebSafeString();
}
//if (nextBatch.size() > 0 )
Entity e = nextBatch.get(0);
Question qs = new Question();
if (e != null) {
if (e.getProperty("question") != null)
qs.setQuestion(e.getProperty("question").toString());
if (e.getProperty("answera") != null)
qs.setAnswera(e.getProperty("answera").toString());
if (e.getProperty("answerb") != null)
qs.setAnswerb(e.getProperty("answerb").toString());
if (e.getProperty("answerc") != null)
qs.setAnswerc(e.getProperty("answerc").toString());
if (e.getProperty("answerd") != null)
qs.setAnswerc(e.getProperty("answerd").toString());
if (e.getProperty("correctanswer") != null)
qs.setQuestion(e.getProperty("correctanswer").toString());
qs.setQuestionNumber(e.getKey().getId());
}
if (encodedCursortmp != null)
qs.setEncodedCursor(encodedCursortmp);
else
qs.setEncodedCursor(encodedCursor);
return qs;
}
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