# Creating GraphQL resolver

The ScandiPWA works by communicating with the server using JSON. This JSON is transferred using the GraphQL API. GraphQL is a replacement to the old, good REST API.

At some point of time, we come to a point, where current schema is just not providing us enough information. What to do in such cases? Keep calm and implement Magento 2 GraphQL resolver!

{% embed url="<https://youtu.be/RPE36f0xQRI>" %}
Working with GraphQL
{% endembed %}

## General rule

Imagine having a normal Magento module. With some model, helpers.

Start with creating a module called `<MODULE_NAME>GraphQL`. Use an [online generator](https://mage2gen.com/) for that

Next, define what would you like to expose! Now, define a schema in `<MODULE_ROOT>/etc/schema.graphqls`. The general docs on doing that can be found on the [official GraphQL site](https://graphql.org/learn/schema/). But, there are few differences in Magento 2:

* The interface implementation does not require to implement all interface fields in the type
* The `extend type` notation is not obligatory, but we recommend using it do distinguish between new and extended types
* The [query caching mechanism](https://devdocs.magento.com/guides/v2.3/graphql/develop/create-graphqls-file.html#query-caching) is not utilized in ScandiPWA, we include all white-listed models which were loaded during the response preparation
* You can use directives like `@resolver` and `@doc` to connect resolvers and document the code quickly

Time to implement the resolver! Connect it with you schema declaration using `@resolver` directive in the schema. Provide a class in the following manner:

```javascript
type Query {
    serverTime: String @resolver(class: "ScandiPWA\\ServerTime\\Model\\Resolver\\ServerTime") @doc(description: "The current server time formatted in YYYY/MM/DD")
}
```

Awesome, now create the resolver class. This should be done in `<MODULE_ROOT>/Model/Resolver/<RESOLVER_NAME>.php`. This should be a class, use following template:

```php
<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */
declare(strict_types=1);

namespace <VENDOR>\<NAME>\Model\Resolver;

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

/**
 * @inheritdoc
 */
class <RESOLVER_NAME> implements ResolverInterface
{
    /**
     * @inheritdoc
     */
    public function resolve(
        Field $field,
        $context,
        ResolveInfo $info,
        array $value = null,
        array $args = null
    ) {
        // resolver functionality ...
    }
}
```

{% hint style="warning" %}
**Note:**

Do not write the complex business logic inside, just refer the original Models.
{% endhint %}

## Advanced performance optimization

The Magento, by default, has the **Batch resolver interface** - read more about these [here](https://devdocs.magento.com/guides/v2.3/graphql/develop/resolvers.html#batchresolverinterface). We are not utilizing them, we started long before they appeared. This is why we now have the [performance module](https://github.com/scandipwa/performance).

{% hint style="warning" %}
**Note:**

We have not dug deep into the new Magento approach to the GraphQL performance issues (Batch resolver interface).
{% endhint %}

Our solution (the performance package) was tested under the 500 RPS (Request Per Second) no cache load. The average response time for category page of 24 products - 0.5s. We can have not validated the performance of Magento resolvers after the `2.3.4`. On `2.3.3` it was not that great.


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