with relation in laravel code example

Example 1: laravel where on relation

Event::whereHas('participants', function ($query) {
    $query->where('IDUser', '=', 1);
})->get();

Example 2: laravel relation of relation

//Multiple relationships:
$books = Book::with('author', 'publisher')->get();

//Nested relationships:
$books = Book::with('author.contacts')->get();