Factory Muffin relationships are "null" when using instance method - php

Question

I'm working on a Laravel 5 app using the jenssegers\laravel-mongodb package and I'm trying to get up and running with Factory Muffin to help with rapidly testing and seeding etc.
I have defined relationships in my factory definitions (code below) - and they work when I run seeds to create new records in the database. By "work", I mean they attach related data correctly to the parent model and persist all those records to the database. But they do not work when I run the $muffin->instance('My\Object') method, which creates a new instance without persisting it. All the relations come back as null.
In a way this makes sense. When the models are stored in the database, they are related by the object _id key. That key doesn't exist until the model is stored. So when I call the instance method, I actually can see via debugging that it does generate the models that would be related, but it does not yet have any key to establish the relation, so that data just kinda goes poof.
This is a bummer because I'd like to be able to generate a fully fleshed-out model with its relations and see for example whether it is saved or passes validation and whatnot when I submit its data to my routes and things. I.e., right now I would not be able to check that the contact's email was valid, etc.
Simplified code samples are below - am I going about this in an entirely wrong way? This is my first time working with Mongo and Factory Muffin. Should this even be able to work the way I want it to?
// factories/all.php
$fm->define('My\Models\Event', [
'title' => Faker::text(75),
'contact' => 'factory|My\Models\Contact'
]);
$fm->define('My\Models\Contact', [
'first_name' => Faker::firstName(),
'email' => Faker::email(),
... etc
]);
// EventControllerTest.php
...
/**
* #var League\FactoryMuffin\FactoryMuffin
*/
protected $muffin;
public function setUp()
{
parent::setUp();
$this->muffin = new FactoryMuffin();
$this->muffin->loadFactories(base_path('tests/factories'));
}
...
public function testCanStoreEvent()
{
$event = $this->muffin->instance('Quirks\Models\Event');
echo $event->contact; // returns null
$event_data = $event->toArray();
$this->call('POST', 'events', $event_data);
$retrieved_event = Event::where('title', '=', $event->title)->get()->first();
$this->assertNotNull($retrieved_event); // passes
$this->assertRedirectedToRoute('events.edit', $retrieved_event->id); // passes
// So, the event is persisted and the controller redirects etc
// BUT, related data is not persisted
}

Answer 1

Ok, in order to get factory muffin to properly flesh out mongo embedded relationships, you have to do like this:
// factories/all.php
$embedded_contact = function() {
$definitions = [
'first_name' => Faker::firstName(),
'email' => Faker::email(),
// ... etc
];
return array_map(
function($item) { return $item(); },
$definitions
);
}
$fm->define('My\Models\Event', [
'title' => Faker::text(75),
'contact' => $embedded_contact
]);
If that seems onerous and hacky ... I agree! I'm definitely interested to hear of easier methods for this. For now I'm proceeding as above and it's working for both testing and seeding.