Fixed variant collection

Author: VoronoyAlexandr

app/code/Magento/ConfigurableProductGraphQl/Model/Resolver/ConfigurableVariant.php

@@ -85,7 +85,7 @@ public function resolve(Field $field, $context, ResolveInfo $info, array $value
             return $this->valueFactory->create($result);
         }
 
-        $this->variantCollection->addParentId((int)$value[$linkField]);
+        $this->variantCollection->addParentId($value['model']);
         $fields = $this->getProductFields($info);
         $matchedFields = $this->attributeCollection->getRequestAttributes($fields);
         $this->variantCollection->addEavAttributes($matchedFields);

app/code/Magento/ConfigurableProductGraphQl/Model/Resolver/Variant/Attributes.php

@@ -35,12 +35,12 @@ public function resolve(
         $data = [];
         foreach ($value['options'] as $option) {
             $code = $option['attribute_code'];
-            if (!isset($value['product'][$code])) {
+            if (!isset($value['product']['model'][$code])) {
                 continue;
             }
 
             foreach ($option['values'] as $optionValue) {
-                if ($optionValue['value_index'] != $value['product'][$code]) {
+                if ($optionValue['value_index'] != $value['product']['model'][$code]) {
                     continue;
                 }
                 $data[] = [

app/code/Magento/ConfigurableProductGraphQl/Model/Variant/Collection.php

@@ -47,9 +47,9 @@ class Collection
     private $metadataPool;
 
     /**
-     * @var int[]
+     * @var Product[]
      */
-    private $parentIds = [];
+    private $parentProduct = [];
 
     /**
      * @var array
@@ -83,18 +83,18 @@ public function __construct(
     }
 
     /**
-     * Add parent Id to collection filter
+     * Add parent to collection filter
      *
-     * @param int $id
+     * @param Product $product
      * @return void
      */
-    public function addParentId(int $id) : void
+    public function addParentId(Product $product) : void
     {
-        if (!in_array($id, $this->parentIds) && !empty($this->childrenMap)) {
+        if (!in_array($product, $this->parentProduct) && !empty($this->childrenMap)) {
             $this->childrenMap = [];
-            $this->parentIds[] = $id;
-        } elseif (!in_array($id, $this->parentIds)) {
-            $this->parentIds[] = $id;
+            $this->parentProduct[] = $product;
+        } elseif (!in_array($product, $this->parentProduct)) {
+            $this->parentProduct[] = $product;
         }
     }
 
@@ -130,20 +130,24 @@ public function getChildProductsByParentId(int $id) : array
      * Fetch all children products from parent id's.
      *
      * @return array
+     * @throws \Exception
      */
     private function fetch() : array
     {
-        if (empty($this->parentIds) || !empty($this->childrenMap)) {
+        if (empty($this->parentProduct) || !empty($this->childrenMap)) {
             return $this->childrenMap;
         }
 
         $linkField = $this->metadataPool->getMetadata(ProductInterface::class)->getLinkField();
-        foreach ($this->parentIds as $id) {
+        foreach ($this->parentProduct as $product) {
+
+            $attributeData = $this->getAttributesCode($product);
             /** @var ChildCollection $childCollection */
             $childCollection = $this->childCollectionFactory->create();
+            $childCollection->addAttributeToSelect($attributeData);
+
             /** @var Product $product */
-            $product = $this->productFactory->create();
-            $product->setData($linkField, $id);
+            $product->setData($linkField, $product->getId());
             $childCollection->setProductFilter($product);
 
             /** @var Product $childProduct */
@@ -160,4 +164,24 @@ private function fetch() : array
 
         return $this->childrenMap;
     }
+
+    /**
+     * Get attributes code
+     *
+     * @param \Magento\Catalog\Model\Product $currentProduct
+     * @return array
+     */
+    private function getAttributesCode(Product $currentProduct): array
+    {
+        $attributeCode = [];
+        $allowAttributes = $currentProduct->getTypeInstance()->getConfigurableAttributes($currentProduct);
+        foreach ($allowAttributes as $attribute) {
+            $productAttribute = $attribute->getProductAttribute();
+            if (!\in_array($productAttribute->getAttributeCode(), $attributeCode)) {
+                $attributeCode[] = $productAttribute->getAttributeCode();
+            }
+        }
+
+        return $attributeCode;
+    }
 }