/* * 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 datafu.pig.bags; import java.io.IOException; import java.util.Arrays; import org.apache.pig.data.BagFactory; import org.apache.pig.data.DataBag; import org.apache.pig.data.DataType; import org.apache.pig.data.Tuple; import org.apache.pig.data.TupleFactory; import org.apache.pig.impl.logicalLayer.FrontendException; import org.apache.pig.impl.logicalLayer.schema.Schema; import datafu.pig.util.ContextualEvalFunc; /** * For an empty bag, inserts a tuple having null values for all fields; * otherwise, the input bag is returned unchanged. * * <p> * This can be useful when performing FLATTEN on a bag from a COGROUP, * as FLATTEN on an empty bag produces no data. * </p> */ public class EmptyBagToNullFields extends ContextualEvalFunc<DataBag> { @Override public DataBag exec(Tuple tuple) throws IOException { if (tuple.size() == 0 || tuple.get(0) == null) return null; Object o = tuple.get(0); if (o instanceof DataBag) { DataBag bag = (DataBag)o; if (bag.size() == 0) { // create a tuple with null values for all fields int tupleSize = (Integer)getInstanceProperties().get("tuplesize"); return BagFactory.getInstance().newDefaultBag(Arrays.asList(TupleFactory.getInstance().newTuple(tupleSize))); } else { return bag; } } else throw new IllegalArgumentException("expected a null or a bag"); } @Override public Schema outputSchema(Schema input) { try { if (input.size() != 1) { throw new RuntimeException("Expected only a single field as input"); } if (input.getField(0).type != DataType.BAG) { throw new RuntimeException("Expected a BAG as input, but found " + DataType.findTypeName(input.getField(0).type)); } // get the size of the tuple within the bag int innerTupleSize = input.getField(0).schema.getField(0).schema.getFields().size(); getInstanceProperties().put("tuplesize", innerTupleSize); } catch (FrontendException e) { throw new RuntimeException(e); } return input; } }