RavenOverflow.Services.UserService.CreateOrUpdate C# (CSharp) Method

        public User CreateOrUpdate(OAuthData oAuthData, string userName, string fullName, string email)
        {
            // Lets find an existing user for the provider OR the email address if the provider doesn't exist.
            User user = DocumentSession
                            .Query<User>()
                            .SingleOrDefault(x =>
                                             x.OAuthData.Any(y => y.Id == oAuthData.Id &&
                                                                  y.OAuthProvider == oAuthData.OAuthProvider)) ??
                        DocumentSession
                            .Query<User>()
                            .SingleOrDefault(x => x.Email == email);

            if (user != null)
            {
                // User exists, so lets update the OAuth data, for this user.
                if (user.OAuthData != null)
                {
                    OAuthData existingProvider =
                        user.OAuthData.SingleOrDefault(x => x.OAuthProvider == oAuthData.OAuthProvider);
                    if (existingProvider != null)
                    {
                        user.OAuthData.Remove(existingProvider);
                    }
                }
                else
                {
                    user.OAuthData = new List<OAuthData>();
                }

                user.OAuthData.Add(oAuthData);
            }
            else
            {
                // Ok. No user at all. We create one and store it.
                user = new User
                           {
                               DisplayName = userName,
                               Email = email,
                               Id = null,
                               FullName = fullName,
                               CreatedOn = DateTime.UtcNow,
                               IsActive = true,
                               OAuthData = new List<OAuthData>(),
                               FavoriteTags = new List<string> {"ravendb", "c#", "asp.net-mvc3"}
                           };
                user.OAuthData.Add(oAuthData);
            }

            DocumentSession.Store(user);

            return user;
        }

        private Core.Entities.User AcceptFacebookOAuthToken(FacebookOAuthResult facebookOAuthResult)
        {
            Condition.Requires(facebookOAuthResult).IsNotNull();

            // Grab the code.
            string code = facebookOAuthResult.Code;

            // Grab the access token.
            FacebookOAuthClient facebookOAuthClient = FacebookOAuthClient;
            dynamic result = facebookOAuthClient.ExchangeCodeForAccessToken(code);

            var oauthData = new OAuthData
            {
                OAuthProvider = OAuthProvider.Facebook,
                AccessToken = result.access_token,
                ExpiresOn = DateTime.UtcNow.AddSeconds(result.expires)
            };

            // Now grab their info.
            var facebookWebClient = new FacebookWebClient(oauthData.AccessToken);
            dynamic facebookUser = facebookWebClient.Get("me");
            oauthData.Id = facebookUser.id;

            // Not sure how to Inject an IUserService because it requires a Session .. which I don't have.
            var userService = new UserService(DocumentSession);

            // Now associate this facebook user to an existing user OR create a new one.
            return userService.CreateOrUpdate(oauthData, facebookUser.username, facebookUser.name, facebookUser.email);
        }