Extend an existing GraphQL schema | Magento 2 Developer Documentation

You can extend the default Magento GraphQL schema to add attributes and data types, modify existing resolver behavior, and add features using other extension points. GraphQL uses stitching to assemble a single unified schema out of the many schemas defined in individual modules. All schema.graphqls files are stitched together to a single schema. In this process, all nodes with the same type (such as type, interface, and enum) and name are stitched together and recursively extended/overridden. This process is similar to how XML merging works.

Extend the schema

The first step to retrieve a custom field in an existing query is to extend the appropriate schema object.

In the following example, we will change the description of an existing field (attribute_set_id) and add a new field (attribute_set_name) to the GraphQL schema for the products query. Common use cases require adding fields to the database. Declarative Schema describes how to add a custom field to the database.

The simplified structure of the query schema to get products is:

schema {
    query: Query
    ...
}

type Query {
    products (...): Products
    ...
}

type Products {
    items: [ProductInterface]
    ...
}

interface ProductInterface {
    id: Int
    name: String
    sku: String
    ...
}

We need to extend the ProductInterface, since that is the schema object for a product. We can do this by creating a schema.graphqls file in our custom module’s (OrangeCo/CustomGQL) etc directory.

OrangeCo_CustomGQL/etc/schema.graphqls

interface ProductInterface {
    attribute_set_id: Int
        @doc(description: "ID of the attribute set assigned to the product")
    attribute_set_name: String
        @doc(description: "Name of attribute set assigned to the product")
        @resolver(class: "\\Orange\\CustomGQL\\Model\\Resolver\\ProductAttributeSetNameResolver")
}

The above schema file is merged with the schema present at Magento_CatalogGraphQl/etc/schema.graphqls which contains the original ProductInterface object. Our schema file contains the following fields:

The attribute_set_id field is already present in the original schema, so the field described in our new schema will override the field present in the ProductInterface object. This example only changes the @doc annotation content to demonstrate how the process works.
The attribute_set_name field is not present in the orignal schema, so the field is added to the ProductInterface object by extending it. For our new field, we set a description and a resolver class to resolve the data to be returned.

Resolve the field value

In the resolver, we get the relevant data based on the $value and $args passed to the resolve method. This can be done using a repository interface or a resource model of the custom field.

In our example scenario, we use Magento\Catalog\Api\AttributeSetRepositoryInterface to get the attribute set name for a given attribute set ID obtained from the $value argument and return that as the resolution for the field.

Orange_CustomGQL/Model/Resolver/ProductAttributeSetNameResolver.php

<?php

namespace Orange\CustomGQL\Model\Resolver;

use Magento\Catalog\Api\AttributeSetRepositoryInterface;
use Magento\Framework\GraphQl\Config\Element\Field;
use Magento\Framework\GraphQl\Query\ResolverInterface;
use Magento\Framework\GraphQl\Schema\Type\ResolveInfo;

/**
 * Class to resolve custom attribute_set_name field in product GraphQL query
 */
class ProductAttributeSetNameResolver implements ResolverInterface
{
    /**
     * @var AttributeSetRepositoryInterface
     */
    private $setRepository;

    public function __construct(AttributeSetRepositoryInterface $setRepository)
    {
        $this->setRepository = $setRepository;
    }

    public function resolve(Field $field, $context, ResolveInfo $info, array $value = null, array $args = null)
    {
        return $this->setRepository->get($value['attribute_set_id'])->getAttributeSetName();
    }
}

Extend the schema

Resolve the field value

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