Deveel.Data.Sql.Query.SubsetNode.Evaluate C# (CSharp) Method

        public override ITable Evaluate(IRequest context)
        {
            var table = Child.Evaluate(context);
            return table.Subset(OriginalColumnNames, AliasColumnNames);
        }

        protected override SqlPreparedStatement PrepareStatement(IExpressionPreparer preparer, IQueryContext context)
        {
            var viewName = context.ResolveTableName(ViewName);

            var queryFrom = QueryExpressionFrom.Create(context, QueryExpression);
            var queryPlan = context.DatabaseContext().QueryPlanner().PlanQuery(context, QueryExpression, null);

            var colList = ColumnNames == null ? new string[0] : ColumnNames.ToArray();

            // Wrap the result around a SubsetNode to alias the columns in the
            // table correctly for this view.
            int sz = colList.Length;
            var originalNames = queryFrom.GetResolvedColumns();
            var newColumnNames = new ObjectName[originalNames.Length];

            if (sz > 0) {
                if (sz != originalNames.Length)
                    throw new InvalidOperationException("Column list is not the same size as the columns selected.");

                for (int i = 0; i < sz; ++i) {
                    var colName = colList[i];
                    newColumnNames[i] = new ObjectName(viewName, colName);
                }
            } else {
                sz = originalNames.Length;
                for (int i = 0; i < sz; ++i) {
                    newColumnNames[i] = new ObjectName(viewName, originalNames[i].Name);
                }
            }

            // Check there are no repeat column names in the table.
            for (int i = 0; i < sz; ++i) {
                var columnName = newColumnNames[i];
                for (int n = i + 1; n < sz; ++n) {
                    if (newColumnNames[n].Equals(columnName))
                        throw new InvalidOperationException(String.Format("Duplicate column name '{0}' in view. A view may not contain duplicate column names.", columnName));
                }
            }

            // Wrap the plan around a SubsetNode plan
            queryPlan = new SubsetNode(queryPlan, originalNames, newColumnNames);

            // We have to execute the plan to get the TableInfo that represents the
            // result of the view execution.
            var table = queryPlan.Evaluate(context);
            var tableInfo = table.TableInfo.Alias(viewName);

            return new Prepared(tableInfo, QueryExpression, queryPlan, ReplaceIfExists);
        }