001/*
002 * Copyright (c) 2016-2017 Chris K Wensel <chris@wensel.net>. All Rights Reserved.
003 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved.
004 *
005 * Project and contact information: http://www.cascading.org/
006 *
007 * This file is part of the Cascading project.
008 *
009 * Licensed under the Apache License, Version 2.0 (the "License");
010 * you may not use this file except in compliance with the License.
011 * You may obtain a copy of the License at
012 *
013 *     http://www.apache.org/licenses/LICENSE-2.0
014 *
015 * Unless required by applicable law or agreed to in writing, software
016 * distributed under the License is distributed on an "AS IS" BASIS,
017 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
018 * See the License for the specific language governing permissions and
019 * limitations under the License.
020 */
021
022package cascading.pipe.assembly;
023
024import java.beans.ConstructorProperties;
025
026import cascading.operation.NoOp;
027import cascading.pipe.Each;
028import cascading.pipe.Pipe;
029import cascading.pipe.SubAssembly;
030import cascading.tuple.Fields;
031
032/**
033 * Class Discard is a {@link cascading.pipe.SubAssembly} that will retain all incoming fields except those given on the constructor.
034 * <p>
035 * Use this pipe to narrow a stream of tuples, removing unused data.
036 *
037 * @see Retain
038 */
039public class Discard extends SubAssembly
040  {
041  @ConstructorProperties({"previous", "discardFields"})
042  public Discard( Pipe previous, Fields discardFields )
043    {
044    super( previous );
045
046    if( discardFields == null )
047      throw new IllegalArgumentException( "discardFields may not be null" );
048
049    setTails( new Each( previous, discardFields, new NoOp(), Fields.SWAP ) );
050    }
051  }