PruneOutputColumns.java

/*
 * Licensed 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 com.facebook.presto.sql.planner.iterative.rule;

import com.facebook.presto.matching.Captures;
import com.facebook.presto.matching.Pattern;
import com.facebook.presto.spi.plan.OutputNode;
import com.facebook.presto.sql.planner.iterative.Rule;
import com.google.common.collect.ImmutableSet;

import static com.facebook.presto.sql.planner.iterative.rule.Util.restrictChildOutputs;
import static com.facebook.presto.sql.planner.plan.Patterns.output;

public class PruneOutputColumns
        implements Rule<OutputNode>
{
    private static final Pattern<OutputNode> PATTERN = output();

    public PruneOutputColumns()
    {
    }

    @Override
    public Pattern<OutputNode> getPattern()
    {
        return PATTERN;
    }

    @Override
    public Result apply(OutputNode outputNode, Captures captures, Context context)
    {
        return restrictChildOutputs(
                context.getIdAllocator(),
                outputNode,
                ImmutableSet.copyOf(outputNode.getOutputVariables()))
                .map(Result::ofPlanNode)
                .orElseGet(Result::empty);
    }
}