public function addUser(User $user): bool
	{
		if(!$this->isPersisted)
		{
			throw new LogicException('You can only add a user to a group that exist in the database.');
		}

		if(!$user->isPersisted())
		{
			throw new LogicException('You can only add a user that exist in the database to a group.');
		}

		return $this->users()->link($user);
	}