laravel automatically merge eloquent 1 to 1 relationship code example

Example 1: how to use where relationship laravel

Event::with(["owner", "participants" => function($q) use($someId){
    $q->where('participants.IdUser', '=', 1);
    //$q->where('some other field', $someId);
}])

Example 2: eloquent relationships

$roles = App\User::find(1)->roles()->orderBy('name')->get();