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/*
 * Copyright 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 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(); }