content: /*
   * Copyright 1999-2017 Alibaba Group Holding Ltd.
   *
   * Licensed 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.alibaba.druid.sql.visitor.functions;
  
  import com.alibaba.druid.sql.ast.SQLExpr;
  import com.alibaba.druid.sql.ast.expr.SQLMethodInvokeExpr;
  import com.alibaba.druid.sql.visitor.SQLEvalVisitor;
  
  import java.util.List;
  
  import static com.alibaba.druid.sql.visitor.SQLEvalVisitor.*;
  
  public class Isnull implements Function {
      public static final Isnull instance = new Isnull();
  
      public Object eval(SQLEvalVisitor visitor, SQLMethodInvokeExpr x) {
          final List<SQLExpr> arguments = x.getArguments();
          if (arguments.isEmpty()) {
              return EVAL_ERROR;
          }
  
          SQLExpr condition = arguments.get(0);
          condition.accept(visitor);
          Object itemValue = condition.getAttributes().get(EVAL_VALUE);
          if (itemValue == EVAL_VALUE_NULL) {
              return Boolean.TRUE;
          } else if (itemValue == null) {
              return null;
          } else {
              return Boolean.FALSE;
          }
      }
  }
  