asterix-runtime/src/main/java/org/apache/asterix/runtime/aggregates/scalar/GenericScalarAggregateFunction.java

/*
 * 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 org.apache.asterix.runtime.aggregates.scalar;

import org.apache.asterix.runtime.aggregates.base.SingleFieldFrameTupleReference;
import org.apache.hyracks.algebricks.common.exceptions.AlgebricksException;
import org.apache.hyracks.algebricks.runtime.base.ICopyAggregateFunction;
import org.apache.hyracks.algebricks.runtime.base.ICopyEvaluator;
import org.apache.hyracks.algebricks.runtime.base.ICopyUnnestingFunction;
import org.apache.hyracks.algebricks.runtime.base.ICopyUnnestingFunctionFactory;
import org.apache.hyracks.data.std.util.ArrayBackedValueStorage;
import org.apache.hyracks.dataflow.common.data.accessors.IFrameTupleReference;

/**
 * Implements scalar aggregates by iterating over a collection with the ScanCollection unnesting function,
 * and applying the corresponding ICopyAggregateFunction to each collection-item.
 */
public class GenericScalarAggregateFunction implements ICopyEvaluator {

    private final ArrayBackedValueStorage listItemOut = new ArrayBackedValueStorage();
    private final ICopyAggregateFunction aggFunc;
    private final ICopyUnnestingFunction scanCollection;

    private final SingleFieldFrameTupleReference itemTuple = new SingleFieldFrameTupleReference();

    public GenericScalarAggregateFunction(ICopyAggregateFunction aggFunc,
            ICopyUnnestingFunctionFactory scanCollectionFactory) throws AlgebricksException {
        this.aggFunc = aggFunc;
        this.scanCollection = scanCollectionFactory.createUnnestingFunction(listItemOut);
        listItemOut.reset();
    }

    @Override
    public void evaluate(IFrameTupleReference tuple) throws AlgebricksException {
        scanCollection.init(tuple);
        aggFunc.init();
        while (scanCollection.step()) {
            itemTuple.reset(listItemOut.getByteArray(), 0, listItemOut.getLength());
            aggFunc.step(itemTuple);
            listItemOut.reset();
        }
        aggFunc.finish();
    }
}