PreparerVisitor.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 System.Collections.Generic;

namespace Deveel.Data.Sql.Expressions {
    class PreparerVisitor : SqlExpressionVisitor {
        private readonly IExpressionPreparer preparer;

        public PreparerVisitor(IExpressionPreparer preparer) {
            this.preparer = preparer;
        }

        public override SqlExpression Visit(SqlExpression expression) {
            if (preparer.CanPrepare(expression))
                expression = preparer.Prepare(expression);

            return base.Visit(expression);
        }

        public override SqlExpression VisitAssign(SqlAssignExpression assign) {
            var reference = assign.ReferenceExpression;
            if (reference != null)
                reference = reference.Prepare(preparer);

            var valueExpression = assign.ValueExpression;
            if (valueExpression != null)
                valueExpression = valueExpression.Prepare(preparer);

            return SqlExpression.Assign(reference, valueExpression);
        }

        private static IEnumerable<T> Prepare<T>(IEnumerable<T> list, IExpressionPreparer preparer)
            where T : IPreparable {
            var newList = new List<T>();
            foreach (var item in list) {
                var newItem = item;
                if (newItem != null) {
                    newItem = (T)newItem.Prepare(preparer);
                }

                newList.Add(newItem);
            }

            return newList.ToArray();
        }

        public override SqlExpression VisitQuery(SqlQueryExpression query) {
            var selectColumns = Prepare(query.SelectColumns, preparer);
            var newExpression = new SqlQueryExpression(selectColumns);

            var where = query.WhereExpression;
            if (where != null)
                where = where.Prepare(preparer);

            newExpression.WhereExpression = where;

            var having = query.HavingExpression;
            if (having != null)
                having = having.Prepare(preparer);

            newExpression.HavingExpression = having;

            var from = query.FromClause;
            if (from != null)
                from = (FromClause) ((IPreparable)from).Prepare(preparer);

            query.FromClause = from;

            var nextComposite = query.NextComposite;
            if (nextComposite != null)
                nextComposite = (SqlQueryExpression) nextComposite.Prepare(preparer);

            query.NextComposite = nextComposite;

            return newExpression;
        }
    }
}