belongsTo(Study::class); } public function recipient(): BelongsTo { return $this->belongsTo(User::class, 'recipient_id'); } public function sender(): BelongsTo { return $this->belongsTo(User::class, 'sender_id'); } protected function casts(): array { return [ 'expires_at' => 'datetime', 'access_flags' => StudyAccessFlags::class, ]; } }