'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):

    (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
