a cleaner way to handle this

[github-actions[bot]]

a cleaner way to handle this

https://github.com/apache/incubator-wayang/blob/d46f3c3f0fb963c2ee2640f00a106042fba55431/wayang-api/wayang-api-sql/src/main/java/org/apache/wayang/api/sql/calcite/rules/WayangRules.java#L134

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 * 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,
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 * See the License for the specific language governing permissions and
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 */

package org.apache.wayang.api.sql.calcite.rules;

import org.apache.calcite.adapter.enumerable.EnumerableConvention;
import org.apache.calcite.plan.Convention;
import org.apache.calcite.plan.RelOptRule;
import org.apache.calcite.plan.RelOptTable;
import org.apache.calcite.rel.RelNode;
import org.apache.calcite.rel.convert.ConverterRule;
import org.apache.calcite.rel.core.TableScan;
import org.apache.calcite.rel.logical.LogicalFilter;
import org.apache.calcite.rel.logical.LogicalJoin;
import org.apache.calcite.rel.logical.LogicalProject;
import org.apache.calcite.rel.logical.LogicalTableScan;
import org.apache.wayang.api.sql.calcite.convention.WayangConvention;
import org.apache.wayang.api.sql.calcite.rel.WayangFilter;
import org.apache.wayang.api.sql.calcite.rel.WayangJoin;
import org.apache.wayang.api.sql.calcite.rel.WayangProject;
import org.apache.wayang.api.sql.calcite.rel.WayangTableScan;
import org.checkerframework.checker.nullness.qual.Nullable;

import java.util.ArrayList;
import java.util.List;

//TODO: split into multiple classes
public class WayangRules {

    private WayangRules(){
    }


    public static final RelOptRule WAYANG_JOIN_RULE = new WayangJoinRule(WayangJoinRule.DEFAULT_CONFIG);
    public static final RelOptRule WAYANG_PROJECT_RULE = new WayangProjectRule(WayangProjectRule.DEFAULT_CONFIG);
    public static final RelOptRule WAYANG_FILTER_RULE =  new WayangFilterRule(WayangFilterRule.DEFAULT_CONFIG);
    public static final RelOptRule WAYANG_TABLESCAN_RULE = new WayangTableScanRule(WayangTableScanRule.DEFAULT_CONFIG);
    public static final RelOptRule WAYANG_TABLESCAN_ENUMERABLE_RULE =
            new WayangTableScanRule(WayangTableScanRule.ENUMERABLE_CONFIG);


    private static class WayangProjectRule extends ConverterRule {

        public static final Config DEFAULT_CONFIG = Config.INSTANCE
                .withConversion(LogicalProject.class,
                        Convention.NONE, WayangConvention.INSTANCE,
                        "WayangProjectRule")
                .withRuleFactory(WayangProjectRule::new);


        protected WayangProjectRule(Config config) {
            super(config);
        }

        public RelNode convert(RelNode rel) {
            final LogicalProject project = (LogicalProject) rel;
            return new WayangProject(
                    project.getCluster(),
                    project.getTraitSet().replace(WayangConvention.INSTANCE),
                    convert(project.getInput(), project.getInput().getTraitSet()
                            .replace(WayangConvention.INSTANCE)),
                    project.getProjects(),
                    project.getRowType());
        }
    }


    private static class WayangFilterRule extends ConverterRule {

        public static final Config DEFAULT_CONFIG = Config.INSTANCE
                .withConversion(LogicalFilter.class,
                        Convention.NONE, WayangConvention.INSTANCE,
                        "WayangFilterRule")
                .withRuleFactory(WayangFilterRule::new);


        protected WayangFilterRule(Config config) {
            super(config);
        }

        @Override
        public RelNode convert(RelNode rel) {
            final LogicalFilter filter = (LogicalFilter) rel;
            return new WayangFilter(
                    rel.getCluster(),
                    rel.getTraitSet().replace(WayangConvention.INSTANCE),
                    convert(filter.getInput(), filter.getInput().getTraitSet().
                            replace(WayangConvention.INSTANCE)),
                    filter.getCondition());
        }

    }

    private static class WayangTableScanRule extends ConverterRule {

        public static final Config DEFAULT_CONFIG = Config.INSTANCE
                .withConversion(LogicalTableScan.class,
                        Convention.NONE, WayangConvention.INSTANCE,
                        "WayangTableScanRule")
                .withRuleFactory(WayangTableScanRule::new);

        public static final Config ENUMERABLE_CONFIG = Config.INSTANCE
                .withConversion(TableScan.class,
                        EnumerableConvention.INSTANCE, WayangConvention.INSTANCE,
                        "WayangTableScanRule1")
                .withRuleFactory(WayangTableScanRule::new);

        protected WayangTableScanRule(Config config) {
            super(config);
        }

        @Override
        public @Nullable RelNode convert(RelNode relNode) {

            TableScan scan = (TableScan) relNode;
            final RelOptTable relOptTable = scan.getTable();

            /**
             * This is quick hack to prevent volcano from merging projects on to TableScans
             * TODO: a cleaner way to handle this
             */
            if(relOptTable.getRowType() == scan.getRowType()) {
                return WayangTableScan.create(scan.getCluster(), relOptTable);
            }
            return null;
        }
    }


    private static class WayangJoinRule extends ConverterRule {

        public static final Config DEFAULT_CONFIG = Config.INSTANCE
                .withConversion(LogicalJoin.class, Convention.NONE,
                        WayangConvention.INSTANCE, "WayangJoinRule")
                .withRuleFactory(WayangJoinRule::new);

        protected WayangJoinRule(Config config) {
            super(config);
        }

        @Override
        public @Nullable RelNode convert(RelNode relNode) {
            LogicalJoin join = (LogicalJoin) relNode;
            List<RelNode> newInputs = new ArrayList<>();
            for(RelNode input : join.getInputs()) {
                if(!(input.getConvention() instanceof WayangConvention)) {
                    input = convert(input, input.getTraitSet().replace(WayangConvention.INSTANCE));
                }
                newInputs.add(input);
            }

            return new WayangJoin(
                    join.getCluster(),
                    join.getTraitSet().replace(WayangConvention.INSTANCE),
                    newInputs.get(0),
                    newInputs.get(1),
                    join.getCondition(),
                    join.getVariablesSet(),
                    join.getJoinType()
            );
        }
    }


}

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