QuerySelectColumns.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;
using System.Diagnostics;
using System.Globalization;

using Deveel.Data;
using Deveel.Data.Sql.Expressions;

namespace Deveel.Data.Sql.Query {
    sealed class QuerySelectColumns {
        private static readonly ObjectName FunctionTableName = new ObjectName("FUNCTIONTABLE");

        private readonly QueryExpressionFrom fromSet;

        private readonly List<SelectColumn> selectedColumns;

        // The count of aggregate and constant columns included in the result set.
        // Aggregate columns are, (count(*), avg(cost_of) * 0.75, etc).  Constant
        // columns are, (9 * 4, 2, (9 * 7 / 4) + 4, etc).

        public QuerySelectColumns(QueryExpressionFrom fromSet) {
            this.fromSet = fromSet;
            selectedColumns = new List<SelectColumn>();
        }

        public void SelectSingleColumn(SelectColumn col) {
            selectedColumns.Add(col);
        }

        private void AddAllFromTable(IFromTableSource table) {
            // Select all the tables
            var columns = table.ColumnNames;
            foreach (ObjectName name in columns) {
                // Make up the SelectColumn
                SqlExpression e = SqlExpression.Reference(name);
                var column = new SelectColumn(e) {
                    ResolvedName = name, 
                    InternalName = name
                };

                // Add to the list of columns selected
                SelectSingleColumn(column);
            }
        }

        public void SelectAllColumnsFromSource(ObjectName tableName) {
            // Attempt to find the table in the from set.
            string schema = null;
            if (tableName.Parent != null)
                schema = tableName.Parent.Name;

            IFromTableSource table = fromSet.FindTable(schema, tableName.Name);
            if (table == null)
                throw new InvalidOperationException(tableName + ".* is not a valid reference.");

            AddAllFromTable(table);
        }

        public void SelectAllColumnsFromAllSources() {
            for (int p = 0; p < fromSet.SourceCount; ++p) {
                IFromTableSource table = fromSet.GetTableSource(p);
                AddAllFromTable(table);
            }
        }

        private SelectColumn PrepareColumn(SelectColumn column, IRequest context, IList<SelectColumn> functionColumns,
            ref int aggregateCount) {
            if (column.Expression is SqlQueryExpression)
                throw new InvalidOperationException("Sub-query expressions are invalid in select columns.");

            SelectColumn newColumn;

            var exp = column.Expression;
            if (exp != null)
                exp = exp.Prepare(fromSet.ExpressionPreparer);

            if (exp is SqlReferenceExpression) {
                var sqlRef = (SqlReferenceExpression) exp;
                var colName = sqlRef.ReferenceName;
                ObjectName resolvedName = null;

                var alias = column.Alias;
                if (String.IsNullOrEmpty(alias)) {
                    resolvedName = colName;
                } else {
                    resolvedName = new ObjectName(alias);
                }

                newColumn = new SelectColumn(exp, alias) {
                    InternalName = colName,
                    ResolvedName = resolvedName
                };
            } else {
                var funcAlias = functionColumns.Count.ToString(CultureInfo.InvariantCulture);
                if (column.Expression.HasAggregate(context)) {
                    aggregateCount++;
                    funcAlias += "_A";
                }

                var alias = column.Alias;
                if (string.IsNullOrEmpty(alias))
                    alias = exp.ToString();

                newColumn = new SelectColumn(exp, alias) {
                    InternalName = new ObjectName(FunctionTableName, funcAlias),
                    ResolvedName = new ObjectName(alias)
                };

                functionColumns.Add(newColumn);
            }

            return newColumn;
        }

        public PreparedQuerySelectColumns Prepare(IRequest context) {
            int aggregateCount = 0;
            var functionColumns = new List<SelectColumn>();
            var preparedColumns = new List<SelectColumn>();
            foreach (var column in selectedColumns) {
                var prepared = PrepareColumn(column, context, functionColumns, ref aggregateCount);
                preparedColumns.Add(prepared);
            }

            return new PreparedQuerySelectColumns(preparedColumns, functionColumns, aggregateCount);
        }
    }
}