circular-laravel.php

<?php

class User extends Model
{
  public function avatar()
  {
    return $this->belongsTo(Avatar::class);
  }
}

class Avatar extends Model
{
  public function uploader()
  {
    return $this->bellongsTo(User::class);
  }
}

$user = new User();
$avatar = new Avatar();

$avatar->uploader()->associate($user);
$user->avatar()->associate($avatar);

$user->toArray(); // Maximum function nesting level of '256' reached
$user->getQueueableRelations(); // Maximum function nesting level of '256' reached
$user->toSearchableArray(); // Maximum function nesting level of '256' reached

So, as noted on Twitter, I wonder if you can solve this by simply breaking the variable reference in PHP. Something like this:

<?php

$user = new User();
$avatar = new Avatar();

$avatar->uploader()->associate($user);
$user->avatar()->associate($avatar->withoutRelations());

Calling withoutRelations() will clone the model and unset all the relationships.

<?php

/**
 * Duplicate the instance and unset all the loaded relations.
 *
 * @return $this
 */
public function withoutRelations()
{
    $model = clone $this;

    return $model->unsetRelations();
}