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A driver for Apache Cassandra 1.2+ that works exclusively with the Cassandra Query Language version 3
(CQL3) and Cassandra's binary protocol.
/*
* Copyright (C) 2012-2017 DataStax Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.datastax.driver.core;
import com.google.common.util.concurrent.ListenableFuture;
import java.util.Iterator;
import java.util.List;
/**
* Defines an iterable whose elements can be remotely fetched and paged,
* possibly asynchronously.
*/
public interface PagingIterable, T> extends Iterable {
/**
* Returns whether this result set has more results.
*
* @return whether this result set has more results.
*/
boolean isExhausted();
/**
* Whether all results from this result set have been fetched from the
* database.
*
* Note that if {@code isFullyFetched()}, then {@link #getAvailableWithoutFetching}
* will return how many rows remain in the result set before exhaustion. But
* please note that {@code !isFullyFetched()} never guarantees that the result set
* is not exhausted (you should call {@link #isExhausted()} to verify it).
*
* @return whether all results have been fetched.
*/
boolean isFullyFetched();
/**
* The number of rows that can be retrieved from this result set without
* blocking to fetch.
*
* @return the number of rows readily available in this result set. If
* {@link #isFullyFetched()}, this is the total number of rows remaining
* in this result set (after which the result set will be exhausted).
*/
int getAvailableWithoutFetching();
/**
* Force fetching the next page of results for this result set, if any.
*
* This method is entirely optional. It will be called automatically while
* the result set is consumed (through {@link #one}, {@link #all} or iteration)
* when needed (i.e. when {@code getAvailableWithoutFetching() == 0} and
* {@code isFullyFetched() == false}).
*
* You can however call this method manually to force the fetching of the
* next page of results. This can allow to prefetch results before they are
* strictly needed. For instance, if you want to prefetch the next page of
* results as soon as there is less than 100 rows readily available in this
* result set, you can do:
*
* ResultSet rs = session.execute(...);
* Iterator<Row> iter = rs.iterator();
* while (iter.hasNext()) {
* if (rs.getAvailableWithoutFetching() == 100 && !rs.isFullyFetched())
* rs.fetchMoreResults();
* Row row = iter.next()
* ... process the row ...
* }
*
* This method is not blocking, so in the example above, the call to {@code
* fetchMoreResults} will not block the processing of the 100 currently available
* rows (but {@code iter.hasNext()} will block once those rows have been processed
* until the fetch query returns, if it hasn't yet).
*
* Only one page of results (for a given result set) can be
* fetched at any given time. If this method is called twice and the query
* triggered by the first call has not returned yet when the second one is
* performed, then the 2nd call will simply return a future on the currently
* in progress query.
*
* @return a future on the completion of fetching the next page of results.
* If the result set is already fully retrieved ({@code isFullyFetched() == true}),
* then the returned future will return immediately but not particular error will be
* thrown (you should thus call {@link #isFullyFetched()} to know if calling this
* method can be of any use}).
*/
ListenableFuture fetchMoreResults();
/**
* Returns the next result from this result set.
*
* @return the next row in this result set or null if this result set is
* exhausted.
*/
T one();
/**
* Returns all the remaining rows in this result set as a list.
*
* Note that, contrary to {@link #iterator()} or successive calls to
* {@link #one()}, this method forces fetching the full content of the result set
* at once, holding it all in memory in particular. It is thus recommended
* to prefer iterations through {@link #iterator()} when possible, especially
* if the result set can be big.
*
* @return a list containing the remaining results of this result set. The
* returned list is empty if and only the result set is exhausted. The result set
* will be exhausted after a call to this method.
*/
List all();
/**
* Returns an iterator over the rows contained in this result set.
*
* The {@link Iterator#next} method is equivalent to calling {@link #one}.
* So this iterator will consume results from this result set and after a
* full iteration, the result set will be empty.
*
* The returned iterator does not support the {@link Iterator#remove} method.
*
* @return an iterator that will consume and return the remaining rows of
* this result set.
*/
Iterator iterator();
/**
* Returns information on the execution of the last query made for this result set.
*
* Note that in most cases, a result set is fetched with only one query, but large
* result sets can be paged and thus be retrieved by multiple queries. In that
* case this method return the {@link ExecutionInfo} for the last query
* performed. To retrieve the information for all queries, use {@link #getAllExecutionInfo}.
*
* The returned object includes basic information such as the queried hosts,
* but also the Cassandra query trace if tracing was enabled for the query.
*
* @return the execution info for the last query made for this result set.
*/
ExecutionInfo getExecutionInfo();
/**
* Return the execution information for all queries made to retrieve this
* result set.
*
* Unless the result set is large enough to get paged underneath, the returned
* list will be singleton. If paging has been used however, the returned list
* contains the {@link ExecutionInfo} objects for all the queries done to obtain this
* result set (at the time of the call) in the order those queries were made.
*
* @return a list of the execution info for all the queries made for this result set.
*/
List getAllExecutionInfo();
}