public static SelectExpression RemoveColumn(this SelectExpression select, ColumnDeclaration column)
{
var columns = new List <ColumnDeclaration>(select.Columns);
columns.Remove(column);
return(select.SetColumns(columns));
}
protected override Expression VisitSelect(SelectExpression select)
{
select = (SelectExpression)base.VisitSelect(select);
// look for redundant column declarations
List <ColumnDeclaration> cols = select.Columns.OrderBy(c => c.Name).ToList();
var removed = new BitArray(select.Columns.Count);
bool anyRemoved = false;
for (int i = 0, n = cols.Count; i < n - 1; i++)
{
ColumnDeclaration ci = cols[i];
var cix = ci.Expression as ColumnExpression;
QueryType qt = cix != null ? cix.QueryType : ci.QueryType;
var cxi = new ColumnExpression(ci.Expression.Type, qt, select.Alias, ci.Name);
for (int j = i + 1; j < n; j++)
{
if (!removed.Get(j))
{
ColumnDeclaration cj = cols[j];
if (SameExpression(ci.Expression, cj.Expression))
{
// any reference to 'j' should now just be a reference to 'i'
var cxj = new ColumnExpression(cj.Expression.Type, qt, select.Alias, cj.Name);
map.Add(cxj, cxi);
removed.Set(j, true);
anyRemoved = true;
}
}
}
}
if (anyRemoved)
{
var newDecls = new List <ColumnDeclaration>();
for (int i = 0, n = cols.Count; i < n; i++)
{
if (!removed.Get(i))
{
newDecls.Add(cols[i]);
}
}
select = select.SetColumns(newDecls);
}
return(select);
}
