/*
* Copyright (c) 2007-2014 Concurrent, Inc. All Rights Reserved.
*
* Project and contact information: http://www.cascading.org/
*
* This file is part of the Cascading project.
*
* 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 cascading.pipe.assembly;
import java.beans.ConstructorProperties;
import cascading.operation.Identity;
import cascading.pipe.Each;
import cascading.pipe.Pipe;
import cascading.pipe.SubAssembly;
import cascading.tuple.Fields;
/**
* Class Retain is a {@link SubAssembly} that will discard all incoming fields except those given on the constructor.
* <p/>
* Use this pipe to narrow a stream of tuples, removing unused data.
*
* @see Discard
*/
public class Retain extends SubAssembly
{
@ConstructorProperties({"previous", "retainFields"})
public Retain( Pipe previous, Fields retainFields )
{
super( previous );
if( retainFields == null )
throw new IllegalArgumentException( "retainFields may not be null" );
setTails( new Each( previous, retainFields, new Identity(), Fields.RESULTS ) );
}
}