Linq Query question

You can do this with the DevForce PredicateBuilder. I'll show you that in a second, but just to cover the other alternatives:

1. You can bring the complete list of entities to the client and filter it there:

      List<string> lastNames = new List<string>();
      lastNames.Add("Davolio");
      lastNames.Add("Fuller");
      lastNames.Add("Buchanan");
      var employees = _mgr.Employees.ToList().Where(e => lastNames.Contains(e.LastName));

2.   You can use a Remote Service Method call to do the above on the server, then ship down only the results;

3.   You can hand-code the query with lots of ORs in the Where clause

      List<Employee> employees = _mgr.Employees.Where(
        e => e.LastName == "Davolio" ||
        e.LastName == "Fuller" ||
        e.LastName == "Buchanan").ToList();

Choices 1 and 3, of course, are either impossible or unacceptable in many scenarios; and choice 2 is maybe more trouble than you'd like to go to. So here's how you do it with the PredicateBuilder, which basically automates the process of  constructing a query like #3:

    private void DoItUsingPredicateBuilder() {
      List<string> lastNames = new List<string>();
      lastNames.Add("Davolio");
      lastNames.Add("Fuller");
      lastNames.Add("Buchanan");

      var tests = EmployeeLastNameTests(lastNames).ToArray();
      if (0 == tests.Length) return;
      var employeeLastNamePredicate = PredicateBuilder.Or(tests);
      List<Employee> employees = _mgr.Employees.Where(employeeLastNamePredicate).ToList();

      //foreach (Employee anEmployee in employees) {
      //  Console.WriteLine(anEmployee.LastName);
      //}
      //PromptToContinue();
    }

    private IEnumerable<Expression<Func<Employee, bool>>> EmployeeLastNameTests(IEnumerable<String> words) {
      foreach (var each in words) {
        var word = each;
        yield return e => e.LastName.Contains(word);
      }
    }

thanks GregD, that's helpful

IdeaBlade.Linq