Using Laravel whenLoaded() deeper than one level - php

Question

How do I use whenLoaded() for deeper than one level relations? It seems as if one can only use whenLoaded with the first relation depth like this:
'season' => $this->whenLoaded('origin', function () {
return new SeasonResource($this->origin->season);
}),
But then Laravel, if origin is loaded, but not season, Laravel will load it, which creates an N+1 problem. Both origin and season relationships are conditional, and not always used. Therefor I want to use something like this:
$this->whenLoaded('origin.season', ...)
or this:
'season' => $this->whenLoaded('origin', function () {
return new SeasonResource($this->origin->whenLoaded('season'));
}),
Neither of these work. I suppose the deeper relations are not stored on the model itself, and in the second case, whenLoaded() does not exists on the query builder.
How do I use whenLoaded() for deeper than one level relations?

Answer 1

I believe the reason this is not implemented is because it only makes sense for hasOne and belongsTo relationships (relationships that return an object, not a collection).
But if that is the case for you, you could do this:
'season' => $this->when(
$this->relationLoaded('origin') &&
$this->origin->relationLoaded('season'),
function () {
return new SeasonResource($this->origin->season);
}
),
Basically, use ->when instead of ->whenLoaded and manually check if the relation is loaded using the ->relationLoaded public method on the model.

Answer 2

For anyone who comes across this and looking for many to many relationships, I've found a solution.
Let's say you've something like
User ---> user_lived_cities ----> city
with table structures as
user_lived_cities
user_id | city_id
------ | ------
cities
id | name
------ | ------
You want to load the cities the user lived in with something like
User::with('livedCities.city')->take(n)->get();
In the resource, you can manipulate the values like this
$livedCityRelation = $this->whenLoaded('livedCities');
$livedCities = $this->when(!empty((array)$livedCityRelation), function () use ($livedCityRelation) {
if ($livedCityRelation instanceof MissingValue) return []; // the relation has no value
$relationLoaded = count($livedCityRelation) /* Remember: It's a collection */ && $livedCityRelation[0]->relationLoaded('city');
return $relationLoaded ? $livedCityRelation->pluck('city') : []; // you can manipulate as per you need. I'm just extracting the city relation from here
});
In your resource in toArray method, you can return
return [
...,
'lived_cities' => City::collection($livedCities),
];
Remember, $livedCities is basically a collection at this point and you can manipulate it as you wish.
If I want to just return an array of city names, I can do that as well with this
$livedCities->pluck('name')
You can apply any collection method that you want to manipulate as per your wish.
Don't forget to import this at the top
use Illuminate\Http\Resources\MissingValue;

Answer 3

You can check for each nested relationship in turn. For example:
$postsLoaded = $user->relationLoaded('posts');
$commentsLoaded = $user->posts->first()->relationLoaded('comments');
$likesLoaded = $user->posts->first()->comments->first()->relationLoaded('likes');
This isn't my solution but it solved my problem - posting so it may help others as this was hard to find. All credit goes to SaeedPrez:
https://laracasts.com/discuss/channels/eloquent/this-relationloaded-for-distant-relationships