einundzwanzig-portal/app/Models/CourseEvent.php

<?php

namespace App\Models;

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

class CourseEvent 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',
        'course_id' => 'integer',
        'venue_id'  => 'integer',
        'from'      => 'datetime',
        'to'        => 'datetime',
    ];

    protected static function booted()
    {
        static::creating(function ($model) {
            if (!$model->created_by) {
                $model->created_by = auth()->id();
            }
        });
    }

    public function createdBy(): BelongsTo
    {
        return $this->belongsTo(User::class, 'created_by');
    }

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

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

    public function registrations(): HasMany
    {
        return $this->hasMany(Registration::class);
    }
}