content: /*
   * 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.calcite.adapter.enumerable;
  
  import org.apache.calcite.plan.Convention;
  import org.apache.calcite.plan.RelTraitSet;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.convert.ConverterRule;
  import org.apache.calcite.rel.core.Union;
  import org.apache.calcite.rel.logical.LogicalUnion;
  import org.apache.calcite.util.Util;
  
  import java.util.List;
  
  /**
   * Rule to convert an {@link LogicalUnion} to an {@link EnumerableUnion}.
   * You may provide a custom config to convert other nodes that extend {@link Union}.
   *
   * @see EnumerableRules#ENUMERABLE_UNION_RULE
   */
  class EnumerableUnionRule extends ConverterRule {
    /** Default configuration. */
    static final Config DEFAULT_CONFIG = Config.INSTANCE
        .withConversion(LogicalUnion.class, Convention.NONE,
            EnumerableConvention.INSTANCE, "EnumerableUnionRule")
        .withRuleFactory(EnumerableUnionRule::new);
  
    /** Called from the Config. */
    protected EnumerableUnionRule(Config config) {
      super(config);
    }
  
    @Override public RelNode convert(RelNode rel) {
      final Union union = (Union) rel;
      final EnumerableConvention out = EnumerableConvention.INSTANCE;
      final RelTraitSet traitSet = rel.getCluster().traitSet().replace(out);
      final List<RelNode> newInputs =
          Util.transform(union.getInputs(), n -> convert(n, traitSet));
      return new EnumerableUnion(rel.getCluster(), traitSet,
          newInputs, union.all);
    }
  }
  