einundzwanzig-portal/app/Models/Registration.php

<?php

namespace App\Models;

use Illuminate\Database\Eloquent\Factories\HasFactory;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Relations\BelongsTo;

class Registration extends Model
{
    use HasFactory;

    /**
     * The attributes that aren't mass assignable.
     * @var array
     */
    protected $guarded = [];

    /**
     * The attributes that should be cast to native types.
     * @var array
     */
    protected $casts = [
        'id'             => 'integer',
        'event_id'       => 'integer',
        'participant_id' => 'integer',
        'active'         => 'boolean',
    ];

    public function courseEvent(): BelongsTo
    {
        return $this->belongsTo(CourseEvent::class);
    }

    public function participant(): BelongsTo
    {
        return $this->belongsTo(Participant::class);
    }
}