Core: cannot perform GraphQL sub-selections on non-resource collections

[ehough]

This issue is related to #2740 and #2687, but it's different enough that I felt it deserves a separate issue.

I'm having trouble performing sub-selection queries on non-doctrine, non-resource collections. Here's an example. Say I have a very simple resource class:

/**
 * @ApiResource
 */
class Book
{
    /**
     * @ApiProperty(identifier=true)
     *
     * @var string
     */
    public $id;

    /**
     * @var Chapter[]
     */
    public $chapters;
}

with Chapter is a simple POPO:

class Chapter
{
    /**
     * @var int
     */
    public $startingPage;

    /**
     * @var string
     */
    public $name;
}

For testing purposes I have custom data provider that serves dummy instances of books, each with several chapters. I also have a Normalizer that handles normalizing Chapters. This works well initially:

But say I want to fetch only the chapter names, I run into the following error:

Field \"chapters\" of type \"Iterable!\" must not have a sub selection.

This is a contrived example, of course, but you can imagine some of the properties on the nested object being bandwidth-heavy or expensive to compute.

I saw that there has been quite a bit of refactoring of the GraphQL code in master, but unfortunately I'm experiencing this issue with both the 2.4 branch as well as master. I also tried to go through the GraphQL code but I'll admit that it's a bit over my head.

Any guidance would be appreciated. Thanks!

[alanpoulain]

Today the schema is built only with the resources. That's why there is this issue.
I plan to do it relatively soon since it's a very asked feature.

[hoangnd25]

Creating a custom type (from ObjectType) then using TypeConverter to replace the default type with the custom type seems to work for me.

[alanpoulain]

Yes it can be a solution.

[ehough]

Creating a custom type (from ObjectType) then using TypeConverter to replace the default type with the custom type seems to work for me.

@hoangnd25 any chance you could share a little pseudo-code showing your custom type and TypeConverter? Would really appreciate any tips you could offer.

[hoangnd25]

You could create custom type like this

<?php

use GraphQL\Type\Definition\ObjectType;
use GraphQL\Type\Definition\Type;

class ChapterType extends ObjectType
{
    public function __construct()
    {
        parent::__construct([
            'name' => 'Chapter',
            'fields' => [
                'startingPage' => [
                    'type' => Type::int(),
                ],
                'name' => [
                    'type' => Type::string()
                ],
            ],
            'resolveField' => [$this, 'resolve']
        ]);
    }

    public function resolve($root, $args, $context, ResolveInfo $resolveInfo)
    {
         if ($resolveInfo->fieldName === 'startingPage') {
                return $root['startingPage'];
         }
    }
}

Then use TypeConverter to replace it

<?php

final class TypeConverter implements TypeConverterInterface
{

    public function convertType(Type $type, bool $input, ?string $queryName, ?string $mutationName, string $resourceClass, string $rootResource, ?string $property, int $depth)
    {
        if (Type::BUILTIN_TYPE_OBJECT === $type->getBuiltinType()
            && is_a($type->getClassName(), Chapter::class, true)
        ) {
            return 'Chapter';

            // or use the type container
            // return $this->typeContainer->get(ChapterType::class)
        }

        return $this->defaultTypeConverter->convertType($type, $input, $queryName, $mutationName, $resourceClass, $rootResource, $property, $depth);
    }
}

You would need to extend ObjectType or equivalent, ApiPlatform\Core\GraphQl\Type\Definition\TypeInterface only works for scalar types

You might need to create a normalizer for Chapter as well.

This is just a hack imo.

[ehough]

Thank you, @hoangnd25! I will give this a shot. I agree that it's a bit of a hack, but hopefully it'll be a stop-gap until @alanpoulain and crew hook us up with a more elegant solution.

You would need to extend ObjectType or equivalent, ApiPlatform\Core\GraphQl\Type\Definition\TypeInterface only works for scalar types

That's where I got hung up before. Thanks for the tip.

[alanpoulain]

Should be solved with https://github.com/api-platform/core/pull/3327.

[wcoppens]

@alanpoulain perhaps you or someone else can share a correct way on configuring the annotations on the model classes? Or is there some example for this case?

Setting the child property to @var ChildClass[] still results in Iterable for me, turning it into Collection<ChildClass> does result in a correct Introspection result however query results are empty in this case while the returned object from the dataprovider definitely isn't.

Tested with api-platform/core version 2.5.4 and 2.5.5

Thanks!

[oleg-brizy]

I had this issue with a regular object type.

<?php

declare(strict_types=1);

namespace App\Type\Definition;

use GraphQL\Type\Definition\ObjectType;
use GraphQL\Type\Definition\Type;
use ApiPlatform\Core\GraphQl\Type\Definition\TypeInterface;

final class SeoPropsType extends ObjectType implements TypeInterface
{
    public function __construct(array $config = [])
    {
        $config['fields'] = [
            'title' => Type::string(),
            'description' => Type::string(),
        ];

        parent::__construct($config);
    }

    public function getName(): string
    {
        return $this->name;
    }

    public function serialize($value)
    {
        return $value;
    }

    public function parseValue($value)
    {
        return $value;
    }

    public function parseLiteral($valueNode, ?array $variables = null)
    {
        return $valueNode;
    }
}

because TypeInterface extends LeafType and it causes the error.

The solution was to not implement TypeInterface and register the type manually
_(because only TypeInterface implementations are registered automatically)_

final class SeoPropsType extends ObjectType { ... }

services:
    App\Type\Definition\SeoPropsType:
      tags: [ 'api_platform.graphql.type' ]

---

Isn't TypeInterface extends LeafType a bug?

Because this is a conflict
MyType extends ObjectType implements TypeInterface🡒LeafType
Object is not a Leaf

[alanpoulain]

@oleg-brizy fixed in https://github.com/api-platform/core/pull/3621.

[oleg-brizy]

@alanpoulain Thanks. But I can't use it because it's not merged and I can't merge it in my fork because I get conflicts.