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.sql2rel;
  
  import org.apache.calcite.plan.RelOptTable;
  import org.apache.calcite.rel.RelNode;
  import org.apache.calcite.rel.type.RelDataType;
  import org.apache.calcite.rex.RexNode;
  import org.apache.calcite.schema.ColumnStrategy;
  import org.apache.calcite.sql.SqlFunction;
  
  import org.checkerframework.checker.nullness.qual.Nullable;
  
  import java.util.List;
  import java.util.function.BiFunction;
  
  /**
   * An implementation of {@link InitializerExpressionFactory} that always supplies NULL.
   */
  public class NullInitializerExpressionFactory implements InitializerExpressionFactory {
  
    public static final InitializerExpressionFactory INSTANCE =
        new NullInitializerExpressionFactory();
  
    public NullInitializerExpressionFactory() {
    }
  
    @SuppressWarnings("deprecation")
    @Override public boolean isGeneratedAlways(RelOptTable table, int iColumn) {
      switch (generationStrategy(table, iColumn)) {
      case VIRTUAL:
      case STORED:
        return true;
      default:
        return false;
      }
    }
  
    @Override public ColumnStrategy generationStrategy(RelOptTable table, int iColumn) {
      return table.getRowType().getFieldList().get(iColumn).getType().isNullable()
          ? ColumnStrategy.NULLABLE
          : ColumnStrategy.NOT_NULLABLE;
    }
  
    @Override public RexNode newColumnDefaultValue(RelOptTable table, int iColumn,
        InitializerContext context) {
      final RelDataType fieldType =
          table.getRowType().getFieldList().get(iColumn).getType();
      return context.getRexBuilder().makeNullLiteral(fieldType);
    }
  
    @Override public @Nullable BiFunction<
        InitializerContext, RelNode, RelNode> postExpressionConversionHook() {
      return null;
    }
  
    @Override public RexNode newAttributeInitializer(RelDataType type,
        SqlFunction constructor, int iAttribute, List<RexNode> constructorArgs,
        InitializerContext context) {
      final RelDataType fieldType =
          type.getFieldList().get(iAttribute).getType();
      return context.getRexBuilder().makeNullLiteral(fieldType);
    }
  }
  