Add using deferrer resolvers and mapping resultsData source

.editorconfig

@@ -0,0 +1,2 @@
+[*.php]
+insert_final_newline = true

.gitignore

@@ -1 +1,3 @@
-.idea/
+.idea/
+vendor/
+composer.lock

README.md

@@ -131,6 +131,118 @@ $apartmentQuery
 $result = $graphQLService->fetch();
 ```
 
+### Querying external related objects using a deferred resolver
+Using deferred resolvers allows to getting relate data by one query after receiving the data of the base query, which solve the N + 1 problem.
+
+Suppose we have next GraphQL query:
+```json
+{
+  wallet {
+    WalletFind {
+      items {
+        id
+        amount
+        company {
+          id
+          title
+        }
+      }
+    }
+  }
+}
+```
+
+Where _company_ object is part of an external service, wich we'd like to get by one query to the external service.
+To solve this problem, we need:
+1. Create CompanyType, which we'd like use in our schema:
+   ```php
+    <?php
+    namespace App\GraphQL\DataSource\Type;
+
+    use Youshido\GraphQL\Field\Field;
+    use Youshido\GraphQL\Type\Object\AbstractObjectType;
+    use Youshido\GraphQL\Type\Scalar\StringType;
+
+    /**
+     * Class CompanyType
+     */
+    class CompanyType extends AbstractObjectType
+    {
+     public function build($config): void
+     {
+   $config->addField(new Field(['name' => 'id', 'type' => new StringType()]))
+    ->addField(new Field(['name' => 'title', 'type' => new StringType()]));
+     }
+    }
+   ```
+
+2. Create CompanyDataSource, which we'd like use to get external data:
+    ```php
+    <?php
+    namespace App\GraphQL\DataSource;
+
+    use \Garlic\Wrapper\Service\GraphQL\DataSource\AbstractDataSource;
+
+    class CompanyDataSource extends AbstractDataSource
+    {
+        public function getQueryName(): string
+        {
+            return 'company.CompanyFind';
+        }
+    }
+    ```
+    We have to create _getQueryName()_ method that returns the name of the query to fetch the companies data.
+
+3. Create WalletCompanyRelation that implements _Garlic\Wrapper\Service\GraphQL\DataSource\DataSourceRelationInterface_ which returns a description of the relation between CompanySource and WalletType.  
+    ```php
+    <?php
+
+    namespace App\GraphQL\DataSource;
+
+    use App\Entity\Wallet;
+    use \Garlic\Wrapper\Service\GraphQL\DataSource\DataSourceRelationInterface;
+
+    class WalletCompanyRelation implements DataSourceRelationInterface
+    {
+        /**
+         * @param Wallet $entity
+         *
+         * @return array
+         */
+        public function relation($entity): array
+        {
+            return ['id' => $entity->getCompanyId()];
+        }
+    }
+    ```
+4. Add the Company field to WalletType:
+    ```php
+    <?php
+
+    namespace App\GraphQL\Type;
+
+    use App\GraphQL\DataSource\CompanyDataSource;
+    use App\GraphQL\DataSource\WalletCompanyRelation;
+    use Garlic\Wrapper\Service\GraphQL\DataSource\DataSourceResolver;
+    use App\GraphQL\DataSource\Type\CompanyType;
+    use Garlic\GraphQL\Type\TypeAbstract;
+    use Youshido\GraphQL\Type\Scalar\FloatType;
+    use Youshido\GraphQL\Type\Scalar\IdType;
+
+    class WalletType extends TypeAbstract
+    {
+        public function build($builder)
+        {
+            $builder->addField('id', new IdType())
+                ->addField('amount', new FloatType(), ['argument' => false])
+                ->addField('company', new CompanyType(), [
+                    'argument' => false,
+                    'resolve' => DataSourceResolver::build(CompanyDataSource::class, WalletCompanyRelation::class),
+                ]);
+        }  
+       //...
+    ```
+
 ### GraphQL mutations
 
 Mutation is the way to change service data by sending some kinds of query. What this queries are and how they could created read below.

Service/GraphQL/DataSource/AbstractDataSource.php

@@ -0,0 +1,136 @@
+<?php
+
+namespace Garlic\Wrapper\Service\GraphQL\DataSource;
+
+use Garlic\Helpers\ArrayHelper;
+use Garlic\Wrapper\Service\GraphQLService;
+
+abstract class AbstractDataSource implements DataSourceInterface
+{
+    /**
+     * @var array
+     */
+    protected $buffer = [];
+
+    /**
+     * @var array|null
+     */
+    protected $result;
+
+    /**
+     * @var string
+     */
+    protected $glueKey = '.';
+
+    /**
+     * @var GraphQLService
+     */
+    private $graphQLService;
+
+    /**
+     * CompanyDataSource constructor.
+     */
+    public function __construct(GraphQLService $graphQLService)
+    {
+        $this->graphQLService = $graphQLService;
+    }
+
+    public function enqueue(array $args): self
+    {
+        if ($this->result !== null) {
+            $this->clear();
+        }
+
+        $this->buffer[] = $args;
+
+        return $this;
+    }
+
+    public function resolve(array $args, array $fields)
+    {
+        if ($this->result === null) {
+            try {
+                $this->result = $this->applyMap($this->fetch($fields));
+            } catch (\Exception $exception) {
+                $this->result = [];
+            }
+        }
+
+        return $this->result[$this->makePKByArgs($args)] ?? null;
+    }
+
+    abstract public function getQueryName(): string;
+
+    protected function clear(): void
+    {
+        $this->buffer = [];
+        $this->result = null;
+    }
+
+    protected function getPrimaryKey(): array
+    {
+        return ['id'];
+    }
+
+    protected function getRelatedFields(array $fields): array
+    {
+        return array_values(array_unique(array_merge($fields, $this->getPrimaryKey())));
+    }
+
+    protected function getRelatedConditions(): array
+    {
+        return array_map(function ($item) {
+            return array_values(array_unique(ArrayHelper::wrap($item)));
+        }, array_merge_recursive(...$this->buffer));
+    }
+
+    protected function getResponseRootPath(): string
+    {
+        return $this->packPath(['data', $this->getQueryName()]);
+    }
+
+    protected function fetch(array $fields): array
+    {
+        $this->graphQLService->createQuery($this->getQueryName())
+            ->select($this->getRelatedFields($fields))
+            ->where($this->getRelatedConditions());
+
+        try {
+            return $this->graphQLService->fetch();
+        } catch (\Exception $exception) {
+            /*
+             * todo[egrik]: add logging exception and retry request
+             */
+        }
+
+        return [];
+    }
+
+    protected function makePKByArgs(array $args): string
+    {
+        $data = ArrayHelper::mapByKeys($args, $this->getPrimaryKey());
+
+        return implode($this->glueKey, array_map(function (...$items) {
+            return implode($this->glueKey, $items);
+        }, array_keys($data), $data));
+    }
+
+    protected function applyMap(array $result): array
+    {
+        $rootItem = ArrayHelper::get($result, $this->getResponseRootPath(), []);
+        $columns = array_map([$this, 'makePKByArgs'], $rootItem);
+
+        return array_map($callback = function ($array) use (&$callback) {
+            if (is_array($array)) {
+                return (object)array_map($callback, $array);
+            }
+
+            return $array;
+        }, array_combine($columns, $rootItem));
+    }
+
+    protected function packPath($items): string
+    {
+        return implode($this->glueKey, $items);
+    }
+}

Service/GraphQL/DataSource/DataSourceInterface.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace Garlic\Wrapper\Service\GraphQL\DataSource;
+
+interface DataSourceInterface
+{
+    public function enqueue(array $args);
+
+    public function resolve(array $args, array $fields);
+}

Service/GraphQL/DataSource/DataSourceRelationInterface.php

@@ -0,0 +1,8 @@
+<?php
+
+namespace Garlic\Wrapper\Service\GraphQL\DataSource;
+
+interface DataSourceRelationInterface
+{
+    public function relation($entity): array;
+}

Service/GraphQL/DataSource/DataSourceResolver.php

@@ -0,0 +1,69 @@
+<?php
+
+namespace Garlic\Wrapper\Service\GraphQL\DataSource;
+
+use Youshido\GraphQL\Execution\DeferredResolver;
+use Youshido\GraphQL\Execution\ResolveInfo;
+use Youshido\GraphQL\Parser\Ast\Field;
+
+class DataSourceResolver
+{
+    /**
+     * @var DataSourceInterface|null
+     */
+    protected $dataSource;
+
+    /**
+     * @var ResolveInfo
+     */
+    protected $resolverInfo;
+
+    protected $value;
+
+    /**
+     * @var DataSourceRelationInterface
+     */
+    private $relation;
+
+    public static function build(string $dataSourceAlias, string $relationAlias): callable
+    {
+        return function ($value, $args, ResolveInfo $resolveInfo) use ($dataSourceAlias, $relationAlias) {
+            $container = $resolveInfo->getContainer();
+
+            return (new static($container->get($dataSourceAlias), $container->get($relationAlias)))(...func_get_args());
+        };
+    }
+
+    /**
+     * DataSourceResolver constructor.
+     */
+    public function __construct(DataSourceInterface $dataSource, DataSourceRelationInterface $relation)
+    {
+        $this->dataSource = $dataSource;
+        $this->relation = $relation;
+    }
+
+    public function __invoke($value, $args, ResolveInfo $resolveInfo): DeferredResolver
+    {
+        $this->resolverInfo = $resolveInfo;
+        $this->value = $value;
+
+        $this->dataSource->enqueue($this->handleRelationCallback());
+
+        return new DeferredResolver(function () {
+            return $this->dataSource->resolve($this->handleRelationCallback(), $this->getFields());
+        });
+    }
+
+    protected function handleRelationCallback(): array
+    {
+        return $this->relation->relation($this->value);
+    }
+
+    protected function getFields(): array
+    {
+        return array_map(function (Field $field) {
+            return $field->getName();
+        }, $this->resolverInfo->getFieldASTList());
+    }
+}

composer.json

@@ -15,13 +15,21 @@
       "Garlic\\Wrapper\\": ""
     }
   },
+  "repositories": [
+    {
+      "type": "vcs",
+      "url": "https://github.com/egrik/helpers.git"
+    }
+  ],
   "require": {
     "php": ">=7.1",
     "garlic/bus": "1.*",
     "jms/serializer-bundle": "^2.0",
     "enqueue/enqueue-bundle": "^0.8",
     "enqueue/amqp-ext": "^0.8",
     "dflydev/dot-access-data": "^2.0",
-    "ext-json": "*"
+    "ext-json": "*",
+    "garlic/graphql": "^1.2",
+    "garlic/helpers": "^1.0"
   }
 }