protected override Expression VisitSelect(SelectExpression select)
{
bool saveIsOuterMostSelect = this.isOuterMostSelect;
try
{
this.isOuterMostSelect = false;
var saveSuppressOrderBy = this.suppressOrderby;
this.suppressOrderby = false;
var saveGatheredOrderings = this.gatheredOrderings;
if (saveSuppressOrderBy)
{
this.gatheredOrderings = null;
this.isOuterMostSelect = true;
}
select = (SelectExpression)base.VisitSelect(select);
this.suppressOrderby = saveSuppressOrderBy;
if (saveSuppressOrderBy)
{
this.gatheredOrderings = saveGatheredOrderings;
}
bool hasOrderBy = select.OrderBy != null && select.OrderBy.Count > 0;
bool hasGroupBy = select.GroupBy != null && select.GroupBy.Count > 0;
bool canHaveOrderBy = saveIsOuterMostSelect || select.Take != null || select.Skip != null;
bool canReceiveOrderings = canHaveOrderBy && !hasGroupBy && !select.IsDistinct && !AggregateChecker.HasAggregates(select) && !suppressOrderby;
if (hasOrderBy)
{
this.PrependOrderings(select.OrderBy);
}
if (select.IsReverse)
{
if (this.gatheredOrderings == null || gatheredOrderings.Count == 0)
{
throw new NotSupportedException(string.Format(Res.OperationNotSupported, "", "Reverse", "if no 'OrderBy' expression."));
}
for (int i = 0, n = this.gatheredOrderings.Count; i < n; i++)
{
var ord = this.gatheredOrderings[i];
this.gatheredOrderings[i] =
new OrderExpression(
ord.OrderType == OrderType.Ascending ? OrderType.Descending : OrderType.Ascending,
ord.Expression
);
}
}
IEnumerable <OrderExpression> orderings = null;
if (canReceiveOrderings)
{
orderings = this.gatheredOrderings;
}
else if (canHaveOrderBy)
{
orderings = select.OrderBy;
}
bool canPassOnOrderings = !saveIsOuterMostSelect && !hasGroupBy && !select.IsDistinct && !suppressOrderby;
ReadOnlyCollection <ColumnDeclaration> columns = select.Columns;
if (this.gatheredOrderings != null)
{
if (canPassOnOrderings)
{
var producedAliases = TableAliasGatherer.Gather(select.From);
// reproject order expressions using this select's alias so the outer select will have properly formed expressions
BindResult project = this.RebindOrderings(this.gatheredOrderings, select.Alias, producedAliases, select.Columns);
this.gatheredOrderings = null;
this.PrependOrderings(project.Orderings);
columns = project.Columns;
}
else
{
this.gatheredOrderings = null;
}
}
if (orderings != select.OrderBy || columns != select.Columns || select.IsReverse)
{
select = new SelectExpression(select.Alias, columns, select.From, select.Where, orderings, select.GroupBy, select.IsDistinct, select.Skip, select.Take, false);
}
return(select);
}
finally
{
this.isOuterMostSelect = saveIsOuterMostSelect;
}
}
public static HashSet<TableAlias> Gather(Expression source)
{
var gatherer = new TableAliasGatherer();
gatherer.Visit(source);
return gatherer.aliases;
}
