com.datastax.oss.driver.api.core.AsyncPagingIterable Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one
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* to you 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,
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* See the License for the specific language governing permissions and
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*/
package com.datastax.oss.driver.api.core;
import com.datastax.oss.driver.api.core.cql.ColumnDefinitions;
import com.datastax.oss.driver.api.core.cql.ExecutionInfo;
import com.datastax.oss.driver.internal.core.AsyncPagingIterableWrapper;
import edu.umd.cs.findbugs.annotations.NonNull;
import edu.umd.cs.findbugs.annotations.Nullable;
import java.util.Iterator;
import java.util.concurrent.CompletionStage;
import java.util.function.Function;
/**
* An iterable of elements which are fetched asynchronously by the driver, possibly in multiple
* requests.
*/
public interface AsyncPagingIterable> {
/** Metadata about the columns returned by the CQL request that was used to build this result. */
@NonNull
ColumnDefinitions getColumnDefinitions();
/** Returns {@linkplain ExecutionInfo information about the execution} of this page of results. */
@NonNull
ExecutionInfo getExecutionInfo();
/** How many rows are left before the current page is exhausted. */
int remaining();
/**
* The elements in the current page. To keep iterating beyond that, use {@link #hasMorePages()}
* and {@link #fetchNextPage()}.
*
* Note that this method always returns the same object, and that that object can only be
* iterated once: elements are "consumed" as they are read.
*/
@NonNull
Iterable currentPage();
/**
* Returns the next element, or {@code null} if the results are exhausted.
*
* This is convenient for queries that are known to return exactly one element, for example
* count queries.
*/
@Nullable
default ElementT one() {
Iterator iterator = currentPage().iterator();
return iterator.hasNext() ? iterator.next() : null;
}
/**
* Whether there are more pages of results. If so, call {@link #fetchNextPage()} to fetch the next
* one asynchronously.
*/
boolean hasMorePages();
/**
* Fetch the next page of results asynchronously.
*
* @throws IllegalStateException if there are no more pages. Use {@link #hasMorePages()} to check
* if you can call this method.
*/
@NonNull
CompletionStage fetchNextPage() throws IllegalStateException;
/**
* If the query that produced this result was a CQL conditional update, indicate whether it was
* successfully applied.
*
* For consistency, this method always returns {@code true} for non-conditional queries
* (although there is no reason to call the method in that case). This is also the case for
* conditional DDL statements ({@code CREATE KEYSPACE... IF NOT EXISTS}, {@code CREATE TABLE... IF
* NOT EXISTS}), for which Cassandra doesn't return an {@code [applied]} column.
*
*
Note that, for versions of Cassandra strictly lower than 2.1.0-rc2, a server-side bug (CASSANDRA-7337) causes this
* method to always return {@code true} for batches containing conditional queries.
*/
boolean wasApplied();
/**
* Creates a new instance by transforming each element of this iterable with the provided
* function.
*
*
Note that both instances share the same underlying data: consuming elements from the
* transformed iterable will also consume them from this object, and vice-versa.
*/
default MappedAsyncPagingIterable map(
Function elementMapper) {
return new AsyncPagingIterableWrapper<>(this, elementMapper);
}
}