public static DbSelectExpression RemoveRedundantFrom(this DbSelectExpression select)
{
if (select.From is DbSelectExpression fromSelect)
{
return(DbSubqueryRemover.Remove(select, fromSelect));
}
return(select);
}
protected override Expression VisitSelect(DbSelectExpression select)
{
select = base.VisitSelect(select) as DbSelectExpression;
var redundant = RedundantSubqueryGatherer.Gather(select.From);
if (redundant != null)
{
select = DbSubqueryRemover.Remove(select, redundant);
}
return(select);
}
protected override Expression VisitProjection(DbProjectionExpression proj)
{
proj = base.VisitProjection(proj) as DbProjectionExpression;
if (proj.Select.From is DbSelectExpression)
{
var redundant = RedundantSubqueryGatherer.Gather(proj.Select);
if (redundant != null)
{
proj = DbSubqueryRemover.Remove(proj, redundant);
}
}
return(proj);
}
protected override Expression VisitSelect(DbSelectExpression select)
{
var wasTopLevel = isTopLevel;
isTopLevel = false;
select = base.VisitSelect(select) as DbSelectExpression;
while (CanMergeWithFrom(select, wasTopLevel))
{
var fromSelect = GetLeftMostSelect(select.From);
select = DbSubqueryRemover.Remove(select, fromSelect);
var where = select.Where;
if (fromSelect.Where != null)
{
if (where != null)
{
where = fromSelect.Where.And(where);
}
else
{
where = fromSelect.Where;
}
}
var orderBy = select.OrderBy != null && select.OrderBy.Count > 0 ? select.OrderBy : fromSelect.OrderBy;
var groupBy = select.GroupBy != null && select.GroupBy.Count > 0 ? select.GroupBy : fromSelect.GroupBy;
var skip = select.Skip ?? fromSelect.Skip;
var take = select.Take ?? fromSelect.Take;
var isDistinct = select.IsDistinct | fromSelect.IsDistinct;
if (where != select.Where || orderBy != select.OrderBy || groupBy != select.GroupBy || isDistinct != select.IsDistinct || skip != select.Skip || take != select.Take)
{
select = new DbSelectExpression(select.Alias, select.Columns, select.From, where, orderBy, groupBy, isDistinct, skip, take, select.IsReverse);
}
}
return(select);
}