I had query that do the job of sorting like the below one

select * from ABC order by isNull(EndDate, '1/1/2079') desc

[EndDate is the small date time column in the ABC table]

I used like this in my C# code SortExpression sorter = new SortExpression(ABCFields.EndDate | SortOperator.Descending);

But i need the sort expression that do the ordering same as the above query that do the sorting with '1/1/2079' when it found null value... Please help me out.

You will ahve to use a DbFunctionCall for the ISNULL() db function. Set this as the expression for the field used in the SortCLause. And you will have to set the sortClause's EmitAliasForExpressionAggregateField property to false.

A similar example can be seen here: http://www.llblgen.com/TinyForum/Messages.aspx?ThreadID=19769