how do I create a custom GraphQL query that fetches a list of products in Magento 2.4.1

Question

In my schema.graphqls file I've created this Query

type Query {
 getLinkedProductsByGroups(groups: [String]): [LinkedProductsByGroup] @resolver(class: "Vendor\\ProductDisplay\\Model\\Resolver\\LinkedProductsByGroups")
}
type LinkedProductsByGroup {
 group: String
 products: [ProductInterface]
}

I've created my resolver

<?php
/*
 * Copyright (c) 2023. Vendor TECHNOLOGIES
 */
namespace Vendor\ProductDisplay\Model\Resolver;
use Vendor\ProductDisplay\Service\LinkedProductsLocator;
use Magento\Catalog\Api\ProductRepositoryInterface;
use Magento\CatalogGraphQl\Model\Resolver\Product\ProductFieldsSelector;
use Magento\CatalogGraphQl\Model\Resolver\Products\DataProvider\Deferred\Product as ProductDataProvider;
use Magento\CatalogGraphQl\Model\Resolver\Products\DataProvider\ProductSearch;
use Magento\Framework\Api\SearchCriteriaBuilderFactory;
use Magento\Framework\GraphQl\Config\Element\Field;
use Magento\Framework\GraphQl\Query\Resolver\BatchResolverInterface;
use Magento\Framework\GraphQl\Query\Resolver\BatchResponse;
use Magento\Framework\GraphQl\Query\Resolver\ContextInterface;
use Magento\Framework\GraphQl\Query\Resolver\ValueFactory;
use Magento\Framework\GraphQl\Query\ResolverInterface;
use Magento\Framework\GraphQl\Schema\Type\ResolveInfo;
class LinkedProductsByGroups implements ResolverInterface
{
 protected LinkedProductsLocator $linkedProductsLocator;
 protected ProductRepositoryInterface $productRepository;
 protected SearchCriteriaBuilderFactory $searchCriteriaBuilderFactory;
 public function __construct(
 SearchCriteriaBuilderFactory $searchCriteriaBuilderFactory,
 ProductRepositoryInterface $productRepository,
 LinkedProductsLocator $linkedProductsLocator
 )
 {
 $this->linkedProductsLocator = $linkedProductsLocator;
 $this->searchCriteriaBuilderFactory = $searchCriteriaBuilderFactory;
 $this->productRepository = $productRepository;
 }
 public function resolve(Field $field, $context, ResolveInfo $info, array $value = null, array $args = null)
 {
 $result = [];
 $groups = $args['groups'];
 foreach ($groups as $group) {
 $resultItem = [];
 $resultItem['group'] = $group;
 $resultItem['products'] = [];
 //fetch related products
 $linkedProductIds = $this->linkedProductsLocator->getLinkedProductIdsByGroup($group);
 $scb = $this->searchCriteriaBuilderFactory->create();
 $scb->addFilter('entity_id', $linkedProductIds, 'in');
 $searchResults = $this->productRepository->getList($scb->create());
 if ($searchResults->getTotalCount() > 0) {
 foreach ($searchResults->getItems() as $item) {
 $data = $item->toArray();
 $data['model'] = 'product';
 $resultItem['products'][] = $data;
 }
 }
 $result[] = $resultItem;
 }
 return $result;
 }
}

This pretty much works but I have a problem fetching composite fields like price or small_image.

When I run my query without them everything is fine.

But with them I get this error

query {
 getLinkedProductsByGroups(groups: ["001021", "001107"]) {
 group
 products { 
 name
 sku
 small_image {
 url
 } 
 }
 }
}

This error comes up

{
 "errors": [
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 0,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 1,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 2,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 3,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 4,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 5,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 6,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 7,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 8,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 9,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 10,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 0,
 "products",
 11,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 1,
 "products",
 0,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 1,
 "products",
 1,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 1,
 "products",
 2,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 1,
 "products",
 3,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 1,
 "products",
 4,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 1,
 "products",
 5,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 1,
 "products",
 6,
 "small_image",
 "url"
 ]
 },
 {
 "debugMessage": "Call to a member function getData() on string",
 "message": "Internal server error",
 "extensions": {
 "category": "internal"
 },
 "locations": [
 {
 "line": 8,
 "column": 11
 }
 ],
 "path": [
 "getLinkedProductsByGroups",
 1,
 "products",
 7,
 "small_image",
 "url"
 ]
 }
 ],
 "data": {
 "getLinkedProductsByGroups": [
 {
 "group": "001021",
 "products": [
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-PKIB",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-PKYW",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-PKDBL",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "BIDI BADU Bella Tech Neck Women's T-shirt-XS",
 "sku": "001021-PKDBL-XS",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-BKDBL",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-DBPK",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-CON",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-GRCO",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-PKGR",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Tech Neck Women's T-shirt-XS",
 "sku": "001021-PKGR-XS",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-RDPK",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Bella Women's Tech Neck T-shirt",
 "sku": "001021-ANDB",
 "small_image": {
 "url": null
 }
 }
 ]
 },
 {
 "group": "001107",
 "products": [
 {
 "name": "Bidi Badu Magu Crew Tech Sport Socks x 3",
 "sku": "001107-WH",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Magu Crew Tech Socks - set of 3-39-42",
 "sku": "001107-WH-39-42",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Magu Crew Tech Socks - set of 3-43-46",
 "sku": "001107-WH-43-46",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Magu Crew Tech Socks - set of 3-46-50",
 "sku": "001107-WH-46-50",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Magu Crew Tech Sport Socks x 3",
 "sku": "001107-BK",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Magu Crew Tech Socks - set of 3-39-42",
 "sku": "001107-BK-39-42",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Magu Crew Tech Socks - set of 3-43-46",
 "sku": "001107-BK-43-46",
 "small_image": {
 "url": null
 }
 },
 {
 "name": "Bidi Badu Magu Crew Tech Socks - set of 3-46-50",
 "sku": "001107-BK-46-50",
 "small_image": {
 "url": null
 }
 }
 ]
 }
 ]
 }
}

Of course I can't use the price / image fields directly because the ProductInterface type must have a sub-selection for them. But the toArray() and the getData() functions don't give the result as expected. So how do I make it convert the fields properly from the ProductInterface defined in the PHP classes, to the ProductInterface defined in GraphQl so that the result is correct?

Answer 1

To answer my own question there is a ProductDataProvider service for requesting the product information by ID.

\Magento\CatalogGraphQl\Model\ProductDataProvider

Using this function

\Magento\CatalogGraphQl\Model\ProductDataProvider::getProductDataById

Makes everything resolve correctly in the GraphQl resolver

Moreover I can modify my code to

 if ($searchResults->getTotalCount() > 0) {
 foreach ($searchResults->getItems() as $item) {
 $data = $item->toArray();
 $data['model'] = $item;
 $resultItem['products'][] = $data;
 }
 }

so that it works as well. The difference is that in the model key, the whole product object needs to be passed.