Add legacy readone graphql resolver (#1260)

_legacy/GraphQL/ReadOneLegacyResolver.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace SilverStripe\Admin\GraphQL;
+
+use GraphQL\Type\Definition\ResolveInfo;
+use SilverStripe\Core\Injector\Injector;
+use SilverStripe\GraphQL\OperationResolver;
+use SilverStripe\GraphQL\Scaffolding\Scaffolders\CRUD\ReadOne;
+use SilverStripe\GraphQL\Scaffolding\StaticSchema;
+use SilverStripe\ORM\DataObject;
+use Symfony\Component\VarDumper\Cloner\Data;
+
+if (!class_exists(ReadOne::class)) {
+    return;
+}
+
+/**
+ * Shim to make readOne work like GraphQL 4
+ *
+ * @deprecated 4.8..5.0 Use silverstripe/graphql:^4 functionality.
+ */
+class ReadOneLegacyResolver implements OperationResolver
+{
+    /**
+     * @var DataObject
+     */
+    protected $dataObject;
+
+    public function __construct(DataObject $dataObject)
+    {
+        $this->dataObject = $dataObject;
+    }
+
+    public function resolve($object, array $args, $context, ResolveInfo $info)
+    {
+        if (!$this->dataObject->canView($context['currentUser'])) {
+            throw new \Exception(sprintf('Cannot view %s', $this->dataObject->singular_name()));
+        }
+
+        $idKey = StaticSchema::inst()->formatField('ID');
+        $id = $args['filter'][$idKey]['eq'];
+        $readOne = Injector::inst()->createWithArgs(ReadOne::class, [$this->dataObject->baseClass()]);
+        unset($args['filter']);
+        $args[$idKey] = $id;
+
+        return $readOne->resolve($object, $args, $context, $info);
+    }
+}