If I want to add following type of check in where clause of a query, can I add a dbfunction call for it with PredicateExpression?

ISNUMERIC(CAST(field1 AS nvarCHAR(15))) = 1

Please note that field1 is a text field

Yes, you can. Please see this example: http://www.llblgen.com/TinyForum/Messages.aspx?ThreadID=16373&StartAtMessage=0&#91460