Can't return multi-level resource/collection through API

Question: How do I return values of a resource through another resource? If I have a pivot table inbetween (many to many relationship), does something change, other than the model function $this->hasMany(AnotherModel::class, 'pivottable') ?

For example:

There's a table called "tags", and another table called "tagtranslations"

"tag" only has an ID and timestamps "tagtranslations" has id, tag_id, title, slug and timestamps

There are TagResource and TagTranslationResource

In TagTranslationResource I'm returning the "toArray"

public function toArray($request)
    {
        return parent::toArray($request);
    }
}

and in TagResource I'm returning

return          
        [
            'id' => $this->id,
            'title' => TagTranslationResource::collection($this->title),
            'slug' =>  TagTranslationResource::collection($this->slug)
        ];

and in Controller I'm calling back Tag with tagtranslations

public function index(Request $request)
    {

        $tags = Tag::with('tagtranslation')->get();
        //return $tags;

        return TagResource::collection($tags);
    }

when, in TagResource I call, for example


return [
  'title' => new TagResource($this->title),
  'slug'  => new TagResource($this->slug)
]

I only get null fields in my JSON api response

and the response I get for the

'title' => TagTranslationResource::collection($this->title)

is an error "Call to a member function first() on null"

Can someone please explain what's happening here? :D I also tried with TagResource::collection(TagTranslation::all())->$this->title

but it can't convert to string

Solution

If i understand it correctly the problem is: TagTranslationResource::collection() expect to receive a collection and you are passing just the title and the slug.

How would I do it:

Controller

public function index(Request $request)
{
  return TagResource::collection(
    Tag::with('tagtranslation')->get()
  );
}

TagResource:

return [ 
  'id' => $this->id,
  'any_other_tag_field' => $this->any_other_tag_field, 
  'tagtranslation' => TagTranslationResource::collection($this->tagtranslation),
];

TagTranslationResource:

return [
  'title' => $this->title,
  'slug'  => $this->slug
]

If you want to know a bit more, here is the link of the official docs

And here an article I wrote about api resources.

I hope it help you.