public  T GetBusinessObject (lambda_criteria)

Employee emp = BOC.GetBusinessObject( Employee.ID=123 )

T GetBusinesObject<T>( Func<T, bool> predicate )
{
    return this.FirstOrDefault( predicate );
}

T GetBusinessObject<T>(Predicate<T> constraint) where T : BO

GetBusinessObject<Employee>( e => e.ID = 123 )

BOC<Employee> boc = ...
// checks exactly 1 match, throws if no match
var emp = boc.Single(e => e.ID = 123);
// checks at most 1 match, null if no match
var emp = boc.SingleOrDefault(e => e.ID = 123);
// checks at least one match, throws if no match
var emp = boc.First(e => e.ID = 123);
// returns first match, null if no match
var emp = boc.FirstOrDefault(e => e.ID = 123);