001/*
002 * Copyright (c) 2007-2015 Concurrent, Inc. All Rights Reserved.
003 *
004 * Project and contact information: http://www.cascading.org/
005 *
006 * This file is part of the Cascading project.
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *     http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020
021package cascading.flow.hadoop.planner.rule.expression;
022
023import cascading.flow.planner.iso.expression.ElementCapture;
024import cascading.flow.planner.iso.expression.ExpressionGraph;
025import cascading.flow.planner.iso.expression.FlowElementExpression;
026import cascading.flow.planner.iso.expression.TypeExpression;
027import cascading.flow.planner.rule.RuleExpression;
028import cascading.flow.planner.rule.expressiongraph.SyncPipeExpressionGraph;
029import cascading.pipe.Group;
030import cascading.pipe.HashJoin;
031import cascading.pipe.Pipe;
032import cascading.tap.Tap;
033
034import static cascading.flow.planner.iso.expression.OrElementExpression.or;
035
036/**
037 *
038 */
039public class BalanceGroupSplitExpression extends RuleExpression
040  {
041  public static final FlowElementExpression SHARED_GROUP = new FlowElementExpression( Group.class );
042
043  public BalanceGroupSplitExpression()
044    {
045    super(
046      new SyncPipeExpressionGraph(),
047
048      // in order to capture out degree in sub-graph, we need to capture at least two successors
049      new ExpressionGraph()
050        .arcs( SHARED_GROUP, or( new FlowElementExpression( HashJoin.class ), new FlowElementExpression( Group.class ), new FlowElementExpression( Tap.class ) ) )
051        .arcs( SHARED_GROUP, or( new FlowElementExpression( HashJoin.class ), new FlowElementExpression( Group.class ), new FlowElementExpression( Tap.class ) ) ),
052
053      // sub-graph to match has out degree captured above
054      new ExpressionGraph()
055        .arcs(
056          new FlowElementExpression( ElementCapture.Primary, Pipe.class, TypeExpression.Topo.SplitOnly )
057        )
058    );
059    }
060  }