Getting number of comments from server object model using SocialCommentManager class

//using Microsoft.Office.Server.SocialData; - include this for SocialCommentManager

// Variable declaration

private SocialCommentManager _commentManager = null;
private Uri _currentUri = null;

_siteId = SPContext.Current.Site.ID;
_webId = SPContext.Current.Web.ID;

SPSecurity.RunWithElevatedPrivileges(delegate()
   {
        using (SPSite site = new SPSite(_siteId))
          {
               using (SPWeb web = site.OpenWeb(_webId))
                {
                    _url = HttpContext.Current.Request.Url.ToString();
                     //Create Service Context
                      SPServiceContext _serviceContext =
                                 SPServiceContext.GetContext(web.Site);
                      if (!string.IsNullOrEmpty(_url))
                         {
                                _currentUri = new Uri(_url);
                                //Initialize SocialCommentManager
                                _commentManager = new
                                  SocialCommentManager(_serviceContext);
                                if (_currentUri != null)
                                {
                                    _totalComments =
                                       _commentManager.GetCount(_currentUri);
                                }
                         }
                }
          }
     });