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.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.LogicalTableScan;
  import org.apache.calcite.schema.QueryableTable;
  import org.apache.calcite.schema.Table;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  /** Planner rule that converts a {@link LogicalTableScan} to an {@link EnumerableTableScan}.
   * You may provide a custom config to convert other nodes that extend {@link TableScan}.
   *
   * @see EnumerableRules#ENUMERABLE_TABLE_SCAN_RULE */
  public class EnumerableTableScanRule extends ConverterRule {
    /** Default configuration. */
    public static final Config DEFAULT_CONFIG = Config.INSTANCE
        .withConversion(LogicalTableScan.class,
            r -> EnumerableTableScan.canHandle(r.getTable()),
            Convention.NONE, EnumerableConvention.INSTANCE,
            "EnumerableTableScanRule")
        .withRuleFactory(EnumerableTableScanRule::new);
  
    protected EnumerableTableScanRule(Config config) {
      super(config);
    }
  
    @Override public @Nullable RelNode convert(RelNode rel) {
      TableScan scan = (TableScan) rel;
      final RelOptTable relOptTable = scan.getTable();
      final Table table = relOptTable.unwrap(Table.class);
      // The QueryableTable can only be implemented as ENUMERABLE convention,
      // but some test QueryableTables do not really implement the expressions,
      // just skips the QueryableTable#getExpression invocation and returns early.
      if (table instanceof QueryableTable || relOptTable.getExpression(Object.class) != null) {
        return EnumerableTableScan.create(scan.getCluster(), relOptTable);
      }
  
      return null;
    }
  }
  