public static SelectExpression RemoveOrderExpression(this SelectExpression select, OrderExpression ordering)
{
if (select.OrderBy != null && select.OrderBy.Count > 0)
{
List <OrderExpression> orderby = new List <OrderExpression>(select.OrderBy);
orderby.Remove(ordering);
return(select.SetOrderBy(orderby));
}
return(select);
}
public static SelectExpression AddOrderExpression(this SelectExpression select, OrderExpression ordering)
{
List <OrderExpression> orderby = new List <OrderExpression>();
if (select.OrderBy != null)
{
orderby.AddRange(select.OrderBy);
}
orderby.Add(ordering);
return(select.SetOrderBy(orderby));
}
protected override Expression VisitSelect(SelectExpression select)
{
// select * from table order by x skip s take t
// =>
// select * from (select top s * from (select top s + t from table order by x) order by -x) order by x
select = (SelectExpression)base.VisitSelect(select);
if (select.Skip != null && select.Take != null && select.OrderBy.Count > 0)
{
var skip = select.Skip;
var take = select.Take;
var skipPlusTake = PartialEvaluator.Eval(Expression.Add(skip, take));
select = select.SetTake(skipPlusTake).SetSkip(null);
select = select.AddRedundantSelect(new TableAlias());
select = select.SetTake(take);
// propogate order-bys to new layer
select = (SelectExpression)OrderByRewriter.Rewrite(select);
var inverted = select.OrderBy.Select(ob => new OrderExpression(
ob.OrderType == OrderType.Ascending ? OrderType.Descending : OrderType.Ascending,
ob.Expression
));
select = select.SetOrderBy(inverted);
select = select.AddRedundantSelect(new TableAlias());
select = select.SetTake(Expression.Constant(0)); // temporary
select = (SelectExpression)OrderByRewriter.Rewrite(select);
var reverted = select.OrderBy.Select(ob => new OrderExpression(
ob.OrderType == OrderType.Ascending ? OrderType.Descending : OrderType.Ascending,
ob.Expression
));
select = select.SetOrderBy(reverted);
select = select.SetTake(null);
}
return(select);
}
