Adds a role to a user.

        :param user: The user to manipulate
        :param role: The role to add to the user

def add_role_to_user(self, user, role):
        """Adds a role to a user.

        :param user: The user to manipulate
        :param role: The role to add to the user
        """
        user, role = self._prepare_role_modify_args(user, role)
        result = self.UserRole.select().where(
            self.UserRole.user == user.id,
            self.UserRole.role == role.id,
        )
        if result.count():
            return False
        else:
            self.put(self.UserRole.create(user=user.id, role=role.id))
            return True