How to eager load a list of ids that are not defined as a relation

[pc386]

I have a table with a column called image_ids. It is of type json, an array of ids. The column is not configured as a relation. However it is a relation to the table images. So each of the image_ids exist in the table images. How can I eager load those so I don't have to query each when requesting it? Currently I have a custom resolve for the images field in my Type. Like this:

public function resolveImagesField($root): array
    {
        $images = [];
        if (!empty($root['image_ids'])) {
            $imageService = app()->make(ImageServiceInterface::class);
            foreach ($root['image_ids'] as $imageId) {
                $images[] = $imageService->getById($imageId)->getUrl();
            }
        }

        return $images;
    }

As you can see for each id in the image_ids, I query the image.
However this is less than optimal since it won't be eager loaded and the performance tanks.

[mfn]

Doesn't your ImageServiceInterface have a getByIds?

But that would only solve it for one element, I assume you return multiple "things" which each have their image_ids, right?

[pc386]

That's an improvment already, but yes there are multiple things with image_ids, and I want those all to be eager loaded

[mfn]

Then you probably need the dataloader approach, which is quite a popular solution for GraphQL and has PHP implementations too.

High level, in your resolver:

• you store the image_ids in your "image data loader" -> you just collect them there
• then you return a new \GraphQL\Deferred()
  • where you passed a closure to the Deferred which
    • also has access to the "image data loader"
    • also pass thru the image_ids you collected before
    • but in here you "resolve" them, e.g. lazy load them

Couple of things to note:

• \GraphQL\Deferred is from the underlying webonyx/graphql-php library and is transparently supported
• I know you said "eager loading" and I responded with "lazy loading"
  The trick here is:
  • the Deferred is called after all image_ids have been collected
  • so when you resolve your actual first image_ids for a specific item, you do in fact load all of them at once (in your most efficient way; but also could just be ->whereIn(…))
  • but for any given resolver you only return the image_ids you collected there

The "image data loader" will only load all your image_ids across all items once (=cache them internally) but return only the once requested by each particulars item resolver.

Hope I could explain it well enough. See also https://webonyx.github.io/graphql-php/data-fetching/#solving-n1-problem