protected virtual Expression VisitBetween(BetweenExpression between)
{
var expr = this.Visit(between.Expression);
var lower = this.Visit(between.Lower);
var upper = this.Visit(between.Upper);
return(this.UpdateBetween(between, expr, lower, upper));
}
protected BetweenExpression UpdateBetween(BetweenExpression between, Expression expression, Expression lower, Expression upper)
{
if (expression != between.Expression || lower != between.Lower || upper != between.Upper)
{
return(new BetweenExpression(expression, lower, upper));
}
return(between);
}
protected override Expression VisitSelect(SelectExpression select)
{
select = (SelectExpression)base.VisitSelect(select);
if (select.Skip != null)
{
SelectExpression newSelect = select.SetSkip(null).SetTake(null);
bool canAddColumn = !select.IsDistinct && (select.GroupBy == null || select.GroupBy.Count == 0);
if (!canAddColumn)
{
newSelect = newSelect.AddRedundantSelect(new TableAlias());
}
var colType = SqlType.Int32;
newSelect = newSelect.AddColumn(new ColumnDeclaration(columnName, new RowNumberExpression(select.OrderBy), colType));
// add layer for WHERE clause that references new rownum column
newSelect = newSelect.AddRedundantSelect(new TableAlias());
newSelect = newSelect.RemoveColumn(newSelect.Columns.Single(c => c.Name == columnName));
var newAlias = ((SelectExpression)newSelect.From).Alias;
ColumnExpression rnCol = new ColumnExpression(typeof(int), colType, newAlias, columnName);
Expression where;
if (select.Take != null)
{
where = new BetweenExpression(rnCol, Expression.Add(select.Skip, Expression.Constant(1)), Expression.Add(select.Skip, select.Take));
}
else
{
where = rnCol.GreaterThan(select.Skip);
}
if (newSelect.Where != null)
{
where = newSelect.Where.And(where);
}
newSelect = newSelect.SetWhere(where);
select = newSelect;
}
return(select);
}
protected virtual bool CompareBetween(BetweenExpression a, BetweenExpression b)
{
return(this.Compare(a.Expression, b.Expression) &&
this.Compare(a.Lower, b.Lower) &&
this.Compare(a.Upper, b.Upper));
}
