How to get users from SharePoint via CSOM?

Question

How can I efficiently grab users (with their properties) from a SharePoint web using CSOM? The code below results in multiple calls to the server (one for each user). It's ridiculously inefficient.

Also, is it possible to perform a Filter on the server?

    public static List<Contact> GetUsers(Uri requestUri, string Filter = "")
    {
        ClientContext context;
        var users = new List<Contact>();
        if (ClientContextUtilities.TryResolveClientContext(requestUri, out context, null))
        {
            using (context)
            {
                var web = context.Web;
                var peopleManager = new PeopleManager(context);

                context.Load(web, w => w.Title, w => w.Description, w => w.SiteUsers);
                var siteUsers = web.SiteUsers;
                context.ExecuteQuery();

                foreach (var user in siteUsers)
                    if (user.PrincipalType == Microsoft.SharePoint.Client.Utilities.PrincipalType.User)
                        if (user.Title.ToLower().Contains(Filter.ToLower()) && !users.Any(x => x.FullName == user.Title))
                        {
                            var userProfile = peopleManager.GetPropertiesFor(user.LoginName);
                            context.Load(userProfile);
                            context.ExecuteQuery();

                            var contact = new Contact() { FullName = user.Title, EmailAddress = user.Email };
                            if (userProfile.IsPropertyAvailable("Title"))
                                contact.Position = userProfile.Title;
                            if (userProfile.IsPropertyAvailable("UserProfileProperties") && userProfile.UserProfileProperties.ContainsKey("WorkPhone"))
                                contact.PhoneNumber = userProfile.UserProfileProperties["WorkPhone"];
                            users.Add(contact);
                        }
            }
        }
        return users;
    }

Answer 1

Major improvements

Since SharePoint CSOM supports Request Batching all the user profiles could be retrieved using a single request, for example instead of:

foreach (var user in siteUsers)
{
   var userProfile = peopleManager.GetPropertiesFor(user.LoginName);
   context.Load(userProfile);
   context.ExecuteQuery();
}

user profiles could be retrieved as:

var userProfilesResult = new List<PersonProperties>(); //for storing user profiles
foreach (var user in siteUsers)
{
   var userProfile = peopleManager.GetPropertiesFor(user.LoginName);
   context.Load(userProfile);
   userProfilesResult.Add(userProfile);
}
context.ExecuteQuery();  //submit a single request 

Minor improvements

1)Since SharePoint CSOM supports CAML queries, the filtering operation could be performed on the server side, for example:

var siteUsers = from user in web.SiteUsers
                    where user.PrincipalType == Microsoft.SharePoint.Client.Utilities.PrincipalType.User
                    select user;
var usersResult = context.LoadQuery(siteUsers);
context.ExecuteQuery();

2)You could also use the following checking to determine whether user profile exist for a specified user:

var hasUserProfile = userProfile.ServerObjectIsNull != null && userProfile.ServerObjectIsNull.Value != true;

Modified example

public static List<Contact> GetUsers(Uri requestUri, ICredentials credentials, string filter = "")
{
        ClientContext context;
        var users = new List<Contact>();
        if (ClientContextUtilities.TryResolveClientContext(requestUri, out context, credentials))
        {
            var userProfilesResult = new List<PersonProperties>();
            using (context)
            {
                var web = context.Web;
                var peopleManager = new PeopleManager(context);


                var siteUsers = from user in web.SiteUsers
                    where user.PrincipalType == Microsoft.SharePoint.Client.Utilities.PrincipalType.User
                    select user;
                var usersResult = context.LoadQuery(siteUsers);
                context.ExecuteQuery();

                foreach (var user in usersResult)
                {
                    if (user.Title.ToLower().Contains(filter.ToLower()) && !users.Any(x => x.FullName == user.Title))
                    {
                        var userProfile = peopleManager.GetPropertiesFor(user.LoginName);
                        context.Load(userProfile);
                        userProfilesResult.Add(userProfile);
                    }
                }
                context.ExecuteQuery();


                var result = from userProfile in userProfilesResult 
                             where userProfile.ServerObjectIsNull != null && userProfile.ServerObjectIsNull.Value != true
                        select new Contact() {
                            FullName = userProfile.Title,
                            EmailAddress = userProfile.Email,
                            Position = userProfile.IsPropertyAvailable("Title") ? userProfile.Title : string.Empty,
                            PhoneNumber = userProfile.IsPropertyAvailable("UserProfileProperties") && userProfile.UserProfileProperties.ContainsKey("WorkPhone") ? userProfile.UserProfileProperties["WorkPhone"] : string.Empty
                        };
                users = result.ToList();
            }
        }
        return users;
 }

Answer 2

When you are in a specific context of a website you can do followings:

using (var ctx = new ClientContext("http://theWebsite"))
{
    var list = ctx.Web.SiteUserInfoList;
    var users = list.GetItems(new CamlQuery());
    ctx.Load(users);
    ctx.ExecuteQuery();

    // do what you want with the users
}