public async Task AddGroup(string clientId, Group group)
        {
            var groupDto = new GroupDto
            {
                Name = group.Name,
                ClientId = clientId
            };

            this.context.Groups.Add(groupDto);
            await this.context.SaveChangesAsync();
        }
        public async Task Delete(string clientId, string groupId)
        {
            if (string.IsNullOrWhiteSpace(clientId))
            {
                throw new ArgumentNullException(nameof(clientId));
            }

            if (string.IsNullOrWhiteSpace(groupId))
            {
                throw new ArgumentNullException(nameof(groupId));
            }

            var groupDto = new GroupDto { Id = int.Parse(groupId) };
            this.context.Groups.Attach(groupDto);
            this.context.Groups.Remove(groupDto);
            await this.context.SaveChangesAsync();
        }