/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* 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,
* 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 org.apache.cassandra.service.pager;
import java.nio.ByteBuffer;
import java.util.Collections;
import java.util.List;
import org.apache.cassandra.db.*;
import org.apache.cassandra.db.filter.SliceQueryFilter;
import org.apache.cassandra.exceptions.RequestValidationException;
import org.apache.cassandra.exceptions.RequestExecutionException;
import org.apache.cassandra.service.StorageProxy;
/**
* Pager over a SliceFromReadCommand.
*/
public class SliceQueryPager extends AbstractQueryPager implements SinglePartitionPager
{
private final SliceFromReadCommand command;
private volatile ByteBuffer lastReturned;
// Don't use directly, use QueryPagers method instead
SliceQueryPager(SliceFromReadCommand command, ConsistencyLevel consistencyLevel, boolean localQuery)
{
super(consistencyLevel, command.filter.count, localQuery, command.ksName, command.cfName, command.filter, command.timestamp);
this.command = command;
}
SliceQueryPager(SliceFromReadCommand command, ConsistencyLevel consistencyLevel, boolean localQuery, PagingState state)
{
this(command, consistencyLevel, localQuery);
if (state != null)
{
lastReturned = state.cellName;
restoreState(state.remaining, true);
}
}
public PagingState state()
{
return lastReturned == null
? null
: new PagingState(null, lastReturned, maxRemaining());
}
protected List<Row> queryNextPage(int pageSize, ConsistencyLevel consistencyLevel, boolean localQuery)
throws RequestValidationException, RequestExecutionException
{
SliceQueryFilter filter = command.filter.withUpdatedCount(pageSize);
if (lastReturned != null)
filter = filter.withUpdatedStart(lastReturned, cfm.comparator);
ReadCommand pageCmd = command.withUpdatedFilter(filter);
return localQuery
? Collections.singletonList(pageCmd.getRow(Keyspace.open(command.ksName)))
: StorageProxy.read(Collections.singletonList(pageCmd), consistencyLevel);
}
protected boolean containsPreviousLast(Row first)
{
return lastReturned != null && lastReturned.equals(isReversed() ? lastName(first.cf) : firstName(first.cf));
}
protected boolean recordLast(Row last)
{
lastReturned = isReversed() ? firstName(last.cf) : lastName(last.cf);
return true;
}
protected boolean isReversed()
{
return command.filter.reversed;
}
}