protected Expression VisitSelect(SelectExpression selectExpression)
{
var changed = false;
var canOptimize = _canOptimize;
var projections = new List <ProjectionExpression>();
_canOptimize = false;
foreach (var item in selectExpression.Projection)
{
var updatedProjection = (ProjectionExpression)Visit(item);
projections.Add(updatedProjection);
changed |= updatedProjection != item;
}
var tables = new List <TableExpressionBase>();
foreach (var table in selectExpression.Tables)
{
var newTable = (TableExpressionBase)Visit(table);
changed |= newTable != table;
tables.Add(newTable);
}
_canOptimize = true;
var predicate = (SqlExpression)Visit(selectExpression.Predicate);
changed |= predicate != selectExpression.Predicate;
var groupBy = new List <SqlExpression>();
_canOptimize = false;
foreach (var groupingKey in selectExpression.GroupBy)
{
var newGroupingKey = (SqlExpression)Visit(groupingKey);
changed |= newGroupingKey != groupingKey;
groupBy.Add(newGroupingKey);
}
_canOptimize = true;
var havingExpression = (SqlExpression)Visit(selectExpression.Having);
changed |= havingExpression != selectExpression.Having;
var orderings = new List <OrderingExpression>();
_canOptimize = false;
foreach (var ordering in selectExpression.Orderings)
{
var orderingExpression = (SqlExpression)Visit(ordering.Expression);
changed |= orderingExpression != ordering.Expression;
orderings.Add(ordering.Update(orderingExpression));
}
var offset = (SqlExpression)Visit(selectExpression.Offset);
changed |= offset != selectExpression.Offset;
var limit = (SqlExpression)Visit(selectExpression.Limit);
changed |= limit != selectExpression.Limit;
_canOptimize = canOptimize;
// we assume SelectExpression can always be null
// (e.g. projecting non-nullable column but with predicate that filters out all rows)
_isNullable = true;
return(changed
? selectExpression.Update(
projections, tables, predicate, groupBy, havingExpression, orderings, limit, offset, selectExpression.IsDistinct,
selectExpression.Alias)
: selectExpression);
}
