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.operation;
022
023import cascading.tuple.Fields;
024import cascading.tuple.TupleEntry;
025import cascading.tuple.TupleEntryCollector;
026
027/**
028 * Interface AggregatorCall provides access to the current {@link Aggregator} invocation arguments.
029 * <p/>
030 * This interface is generic, allowing the user to set a custom 'context' object when {@link Aggregator#start(cascading.flow.FlowProcess, AggregatorCall)}
031 * is called. The {@link OperationCall#setContext(Object)} and {@link OperationCall#getContext()} methods are
032 * inherited from {@link OperationCall}.
033 *
034 * @see Aggregator
035 * @see OperationCall
036 */
037public interface AggregatorCall<C> extends OperationCall<C>
038  {
039  /**
040   * Returns the current grouping {@link TupleEntry}.
041   *
042   * @return TupleEntry
043   */
044  TupleEntry getGroup();
045
046  /**
047   * Returns {@link TupleEntry} of argument values.
048   * <p/>
049   * Will return {@code null} unless called in {@link Aggregator#aggregate(cascading.flow.FlowProcess, AggregatorCall)}.
050   * <p/>
051   * Note that the returned TupleEntry should not be cached (stored in a Collection), nor should the underlying Tuple
052   * instance. Where possible Cascading will re-use both TupleEntry and Tuple instances.
053   * <p/>
054   * To get a safe copy that can be cached, use {@link TupleEntry#getTupleCopy()}.
055   *
056   * @return TupleEntry
057   */
058  TupleEntry getArguments();
059
060  /**
061   * Return the resolved {@link cascading.tuple.Fields} declared by the current {@link Operation}.
062   *
063   * @return Fields
064   */
065  Fields getDeclaredFields();
066
067  /**
068   * Returns the {@link cascading.tuple.TupleEntryCollector} used to emit result values.
069   * <p/>
070   * Will return {@code null} unless called in {@link Aggregator#complete(cascading.flow.FlowProcess, AggregatorCall)}.
071   *
072   * @return TupleCollector
073   */
074  TupleEntryCollector getOutputCollector();
075  }