ConstantSelectNode.cs

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// 
//  Copyright 2010-2015 Deveel
// 
//    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.
//

using System;

using Deveel.Data;
using Deveel.Data.Serialization;
using Deveel.Data.Sql.Expressions;
using Deveel.Data.Sql.Tables;

namespace Deveel.Data.Sql.Query {
    [Serializable]
    class ConstantSelectNode : SingleQueryPlanNode {
        public ConstantSelectNode(IQueryPlanNode child, SqlExpression expression)
            : base(child) {
            Expression = expression;
        }

        private ConstantSelectNode(ObjectData data)
            : base(data) {
            Expression = data.GetValue<SqlExpression>("Expression");
        }

        public SqlExpression Expression { get; private set; }


        public override ITable Evaluate(IRequest context) {
            // Evaluate the expression
            var exp = Expression.Evaluate(context, null);
            if (exp.ExpressionType != SqlExpressionType.Constant)
                throw new InvalidOperationException();

            var v = ((SqlConstantExpression) exp).Value;

            // If it evaluates to NULL or FALSE then return an empty set
            if (v.IsNull || v == false)
                return Child.Evaluate(context).EmptySelect();

            return Child.Evaluate(context);
        }

        protected override void GetData(SerializeData data) {
            data.SetValue("Expression", Expression);
        }
    }
}