public async Task Update(string userId, int value)
        {
            var score = Find(userId);

            if (score == null)
            {
                score = new Score
                {
                    UserId = userId,
                    Value  = value
                };
            }
            else
            {
                score.Value = value;
            }

            db.Scores.AddOrUpdate(score);
            await db.SaveChangesAsync();
        }
        public async Task Update(string userId, string ltiRequestJson)
        {
            var ltiRequestModel = FindElement(userId);

            if (ltiRequestModel == null)
            {
                ltiRequestModel = new LtiRequestModel
                {
                    UserId  = userId,
                    Request = ltiRequestJson
                };
            }
            else
            {
                ltiRequestModel.Request = ltiRequestJson;
            }

            db.LtiRequests.AddOrUpdate(ltiRequestModel);
            await db.SaveChangesAsync();
        }