public void ChangeUserRole(User user, Role newRole)
        {
            var userRole = _userRolesEntities.UserRoles.FirstOrDefault(uR => uR.UserID == user.Id);
            if(userRole == null)
                throw new ArgumentException("Cannot find roles for current user in data base");

            userRole.RoleID = newRole.Id;
            _userRolesEntities.SaveChanges();

            user.SetRole(newRole);
        }
        public User AddNewUser(string name, Role role)
        {
            var entityUser = new Model.Entities.User()
            {
                UserName = name
            };

            var entityUserRole = new Model.Entities.UserRole()
            {
                User = entityUser,
                RoleID = role.Id
            };

            _userRolesEntities.Users.Add(entityUser);
            _userRolesEntities.UserRoles.Add(entityUserRole);
            _userRolesEntities.SaveChanges();

            return UserEntityToModel(entityUser);
        }