mysqldump dumping pivot table ...比x_id IN（id's）更好的东西？

I am working on a backup script that should grab all records belonging to user X on the system, for us to restore later on if there is a need for it. For this I am using mysqldump utility and "--where". Idea is to allow user to back up and restore their data when they want to.

I have quite a few pivot tables that I am having to backup with code similar to below:

    # get list of projects id's
    $projectsArr = $user->projects()->get()->lists('id')->toArray();

    $whereClause = '--where="project_id IN (' . implode(",", $projectsArr) . ')"';
    $table_name = 'project_task';
    $this->createTableBackup($projectsArr, $table_name, $whereClause);

Above code works fine when the list of ID's is around 500, which might not be the case in my situation...

The only solution that I can see at the present moment is adding user_id to every pivot table:

    $whereClause = '--where="user_id = ' . $user->id . '"';
    $table_name = 'project_task';
    $this->createTableBackup($projectsArr, $table_name, $whereClause);

Is there a better solution to my problem besides what I have above?

Below is a snippet of code that I use for the backup:

public function dump($destinationFile, $table_name, $whereClause, $options) {
        $command = sprintf('mysqldump %s --user=%s --password=%s --host=%s --port=%s %s %s %s > %s', $options, escapeshellarg($this->user), escapeshellarg($this->password), escapeshellarg($this->host), escapeshellarg($this->port), escapeshellarg($this->database), escapeshellarg($table_name), escapeshellarg($whereClause), escapeshellarg($destinationFile)
        ); 
        return $this->run($command);
    }