Prevent deletion of parent if it has child records

Let's say we have model User and Comment. I want to prevent deletion user if he has comments. To do so we need to look at model events at laravel's doc

Example

class User extends Eloquent
{
    public function comments()
    {
        return $this->has_many('Comment');
    }

    protected static function boot() {
        parent::boot();

        static::deleting(function($user) {
             if ($user->comments()->count() > 0)
            {
                throw new Exception("Model have child records");
            }
        });
    }
}

P.S. english is not my native language