C# in Depth

LINQ beyond .NET 3.5347LINQ TO ACTIVE DIRECTORYAlmost all companies running their IT infrastructure on Windows use Active Directoryto manage users, computers, settings, and more. Active Directory is a directoryserver that implements LDAP as one query protocol, but other LDAP servers are available,including the free OpenLDAP platform. 8Bart De Smet 9 (who now works for Microsoft) implemented a prototype LINQ toActive Directory provider as a tutorial on how LINQ providers work—but it has alsoproved to be a valuable reminder of how broadly LINQ is targeted. Despite the name,it is capable of querying non-Microsoft servers. He has also repeated the feat with aLINQ to SharePoint provider, which we won’t cover here, but which is a more completeprovider implementation.If you’re not familiar with directories, you can think of them as a sort of cross betweenfile system directory trees and databases. They form hierarchies rather than tables, buteach node in the tree is an entity with properties and an associated schema. (For thoseof you who are familiar with directories, please forgive this gross oversimplification.)Installing and populating a directory is a bit of an effort, so for the sample codeI’ve connected to a public server. If you happen to have access to an internal server,you’ll probably find the results more meaningful if you connect to that.Listing 12.21 connects to an LDAP server and lists all the users whose first namebegins with K. The Person type is described elsewhere in the sample source code,complete with attributes to describe to LINQ to Active Directory how the propertieswithin the object map to attributes within the directory.Listing 12.21LINQ to Active Directory sample, querying users by first namestring url = "LDAP://ldap.andrew.cmu.edu/dc=cmu,dc=edu";DirectoryEntry root = new DirectoryEntry(url);root.AuthenticationType = AuthenticationTypes.None;var users = new DirectorySource(root, SearchScope.Subtree);users.Log = Console.Out;var query = from user in userswhere user.FirstName.StartsWith("K")select user;foreach (Person person in query){Console.WriteLine (person.DisplayName);foreach (string title in person.Titles){Console.WriteLine(" {0}", title);}}Are you getting a sense of déjà vu yet? Listing 12.21 shows yet another query expression,which just happens to target LDAP. If you didn’t have the first part, which sets the8www.openldap.org9http://blogs.bartdesmet.net/bartLicensed to Rhona Hadida