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 com.aliyun.odps.lot.operators;
  
  import java.util.List;
  
  import com.aliyun.odps.lot.common.ArgumentNullException;
  import com.aliyun.odps.lot.common.ScalarExpression;
  
  import apsara.odps.lot.Lot;
  import apsara.odps.lot.SelectProtos;
  
  public class Select extends Operator {
  
    public static class Expression {
  
      private String alias;
      private ScalarExpression expression;
  
      public String getAlias() {
        return alias;
      }
  
      public ScalarExpression getExpression() {
        return expression;
      }
  
      public Expression(String alias, ScalarExpression expression) {
        if (alias == null) {
          throw new ArgumentNullException("alias");
        }
  
        if (expression == null) {
          throw new ArgumentNullException("expression");
        }
  
        this.alias = alias;
        this.expression = expression;
      }
    }
  
    private List<Expression> expressions;
  
    public List<Expression> getExpressions() {
      return expressions;
    }
  
    /*
    �����Ǹ�list������map����Ϊ������ĳЩ����������������alias�����������˸�FakeSink/AdhocSink
     */
    public Select(List<Expression> expressions) {
      if (expressions == null) {
        throw new ArgumentNullException("expressions");
      }
  
      if (expressions.size() == 0) {
        throw new IllegalArgumentException(
            "You have to specify one item at least for Select operator.");
      }
  
      this.expressions = expressions;
    }
  
    @Override
    public Lot.LogicalOperator toProtoBuf() {
      assert (getParents().size() == 1);
  
      Lot.LogicalOperator.Builder builder = Lot.LogicalOperator.newBuilder();
      SelectProtos.Select.Builder s = SelectProtos.Select.newBuilder();
      s.setId(getId());
      s.setParentId(getParents().get(0).getId());
  
      for (Expression expr : expressions) {
        SelectProtos.Select.Expressions.Builder e = SelectProtos.Select.Expressions.newBuilder();
        e.setExpression(expr.getExpression().toProtoBuf());
        e.setAlias(expr.getAlias());
        s.addExpressions(e.build());
      }
  
      builder.setSelect(s.build());
  
      return builder.build();
    }
  }
  