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我想使用GAE遊標使用此頁https://cloud.google.com/appengine/docs/standard/java/datastore/query-cursors作爲靈感。 問題是,我的代碼下面返回的遊標爲空 - 我不明白爲什麼,因爲我認爲我使用與上述鏈接相同的結構,即查詢的結果是QueryResultList,並且我使用getCursor方法在結果上獲得對遊標的引用。 NON_SENT_MATCHES_LIMIT是20,如果我對查詢設置了無限制,那麼有超過2000個實體,所以我期望得到一個非空的遊標。爲什麼從我的GAE數據存儲查詢返回遊標爲空?
任何人都可以向我解釋爲什麼遊標爲空?
public ProductRuleMatchWithCursor getNonSentMatchesBatch(Transaction transaction, long shopId, Cursor startCursor) {
Query.FilterPredicate activeOrderProduct = new Query.FilterPredicate(ProductRuleMatchDBFields.ACTIVE, Query.FilterOperator.EQUAL, true);
Query.FilterPredicate pendingOrderProduct = new Query.FilterPredicate(ProductRuleMatchDBFields.MATCH_STATUS, Query.FilterOperator.EQUAL, MatchStatus.PENDING.getId());
Query.FilterPredicate failedOrderProduct = new Query.FilterPredicate(ProductRuleMatchDBFields.MATCH_STATUS, Query.FilterOperator.EQUAL, MatchStatus.FAILED_CAN_RECOVER.getId());
Query query = new Query(ProductRuleMatchDBFields.PRODUCT_RULE_MATCH_TABLE_NAME).setFilter(Query.CompositeFilterOperator.and(activeOrderProduct, Query.CompositeFilterOperator.or(pendingOrderProduct, failedOrderProduct)));
query.setAncestor(KeyFactory.createKey(ShopDBFields.SHOP_TABLE_NAME, shopId));
FetchOptions fetchOptions = FetchOptions.Builder.withLimit(NON_SENT_MATCHES_LIMIT);
if (startCursor != null){
fetchOptions.startCursor(startCursor);
}
QueryResultList<Entity> entities = datastore.prepare(transaction, query).asQueryResultList(fetchOptions);
List<ProductRuleMatch> matches = new ArrayList<>();
for (Entity entity : entities) {
matches.add(createModelFromEntity(entity));
}
Cursor cursor = entities.getCursor();
logger.info("The cursor is: " + cursor);
return new ProductRuleMatchWithCursor(matches, cursor);
}
但是你怎麼做呢,如果你有一個CompositeFilterOperator.or查詢,你需要使用遊標? – Lull