com.datastax.driver.core.PagingIterable Maven / Gradle / Ivy
/*
* 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();
}