SortNode.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.Tables;

namespace Deveel.Data.Sql.Query {
    [Serializable]
    class SortNode : SingleQueryPlanNode {
        public SortNode(IQueryPlanNode child, ObjectName[] columnNames, bool[] ascending) 
            : base(child) {

            // How we handle ascending/descending order
            // ----------------------------------------
            // Internally to the database, all columns are naturally ordered in
            // ascending order (start at lowest and end on highest).  When a column
            // is ordered in descending order, a fast way to achieve this is to take
            // the ascending set and reverse it.  This works for single columns,
            // however some thought is required for handling multiple column.  We
            // order columns from RHS to LHS.  If LHS is descending then this will
            // order the RHS incorrectly if we leave as is.  Therefore, we must do
            // some pre-processing that looks ahead on any descending orders and
            // reverses the order of the columns to the right.  This pre-processing
            // is done in the first pass.

            int sz = ascending.Length;
            for (int n = 0; n < sz - 1; ++n) {
                if (!ascending[n]) {    // if descending...
                    // Reverse order of all columns to the right...
                    for (int p = n + 1; p < sz; ++p) {
                        ascending[p] = !ascending[p];
                    }
                }
            }

            ColumnNames = columnNames;
            Ascending = ascending;
        }

        private SortNode(ObjectData data)
            : base(data) {
            ColumnNames = data.GetValue<ObjectName[]>("Columns");
            Ascending = data.GetValue<bool[]>("Ascending");
        }

        public ObjectName[] ColumnNames { get; private set; }

        public bool[] Ascending { get; private set; }

        public override ITable Evaluate(IRequest context) {
            var t = Child.Evaluate(context);
            return t.OrderBy(ColumnNames, Ascending);
        }

        protected override void GetData(SerializeData data) {
            data.SetValue("Columns", ColumnNames);
            data.SetValue("Ascending", Ascending);
        }
    }
}