phoenix-core/src/main/java/org/apache/phoenix/iterate/FilterAggregatingResultIterator.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.phoenix.iterate;

import java.sql.SQLException;
import java.util.List;

import org.apache.hadoop.hbase.io.ImmutableBytesWritable;
import org.apache.phoenix.expression.Expression;
import org.apache.phoenix.expression.aggregator.Aggregator;
import org.apache.phoenix.schema.tuple.Tuple;
import org.apache.phoenix.schema.types.PBoolean;


/**
 * 
 * Post aggregation filter for HAVING clause. Due to the way we cache aggregation values
 * we cannot have a look ahead for this Iterator, because the expressions in the SELECT
 * clause would return values for the peeked row instead of the current row. If we only
 * use the Result argument in {@link org.apache.phoenix.expression.Expression}
 * instead of our cached value in Aggregators, we could have a look ahead.
 *
 * 
 * @since 0.1
 */
public class FilterAggregatingResultIterator  implements AggregatingResultIterator {
    private final AggregatingResultIterator delegate;
    private final Expression expression;
    private final ImmutableBytesWritable ptr = new ImmutableBytesWritable();
    
    public FilterAggregatingResultIterator(AggregatingResultIterator delegate, Expression expression) {
        this.delegate = delegate;
        this.expression = expression;
        if (expression.getDataType() != PBoolean.INSTANCE) {
            throw new IllegalArgumentException("FilterResultIterator requires a boolean expression, but got " + expression);
        }
    }

    @Override
    public Tuple next() throws SQLException {
        Tuple next;
        do {
            next = delegate.next();
        } while (next != null && expression.evaluate(next, ptr) && Boolean.FALSE.equals(expression.getDataType().toObject(ptr)));
        return next;
    }

    @Override
    public void close() throws SQLException {
        delegate.close();
    }

    @Override
    public Aggregator[] aggregate(Tuple result) {
        return delegate.aggregate(result);
    }

    @Override
    public void explain(List<String> planSteps) {
        delegate.explain(planSteps);
        planSteps.add("CLIENT FILTER BY " + expression.toString());
    }

	@Override
	public String toString() {
		return "FilterAggregatingResultIterator [delegate=" + delegate
				+ ", expression=" + expression + ", ptr=" + ptr + "]";
	}
}