Extension attribute error "Call to undefined method Magento\Catalog\Api\Data\ProductExtension: : setDummyAttribute() on ProductExtension"

Question

Error : Uncaught Error: Call to undefined method Magento\Catalog\Api\Data\ProductExtension: : setDummyAttribute() on ProductExtension in MyCompany\MyModule\Plugin\DummyAttribute"

This is how I have implemented extension attribute.

1. I have used \Magento\Catalog\Model\ResourceModel\Product\CollectionFactory in my function to fetch collection.

2. I have created custom data interface named CustomProductInterface to return my custom data.

3. Basically I am not returning \Magento\Catalog\Api\Data\ProductInterface and instead returning my CustomProductInterface.

4. Everything is working fine so far. Now I am creating extension attribute on CustomProductInterface. After adding this attribute, it starts throwing exception as "call to undefined method getDummyAttribute() on ProductExtension"

After debugging a lot, I found that CustomProductInterface is internally called as interface and corresponding object called is of Magento\Catalog\Api\Data\ProductExtension and not MyCompany\MyModule\Api\Data\CustomProductExtension.

<extension_attributes for="MyCompany\MyModule\Api\Data\CustomProductInterface">
    <attribute code="dummy_attributte" type="string"/>
</extension_attributes>

It works fine If I set extension_attribute for both the Interfaces as mentioned below:

<extension_attributes for="MyCompany\MyModule\Api\Data\CustomProductInterface">
    <attribute code="dummy_attributte" type="string"/>
</extension_attributes>

<extension_attributes for="Magento\Catalog\Api\Data\ProductInterface">
    <attribute code="dummy_attributte" type="string"/>
</extension_attributes>

My requirement is such that I have to use product collection with joins on my custom tables and display required data using my custom interface.

So I have found the solution, but it seems improper to me and I am looking for explanation of above case.

According to my research, it seems like we cannot use extension attribute on custom collection.

Answer 1

I guess I just found the answer. You just have to iterate the core product collection and set the data in your custom interface.

Non-working old code/buggy code :

public function getList(\Magento\Framework\Api\SearchCriteriaInterface $searchCriteria)
    {
       $collection = $this->productCollectionFactory->create();
      /*Join custom data with main/core product collection. */
       $collection = $this->joinExtraTablesForCustomData($collection);
       $searchResult->setSearchCriteria($searchCriteria);
       $searchResult->setItems($collection->getItems());
       $searchResult->setTotalCount($collection->getSize());
       return $searchResult;
    }

The problem in above code is $collection->getItems() will have an array objects of type \Magento\Catalog\Api\Data\ProductInterface. So we have to explicitly change the type to Custom Interface as mentioned below.

This works perfectly fine.

public function getList(\Magento\Framework\Api\SearchCriteriaInterface $searchCriteria)
{
   $collection = $this->productCollectionFactory->create();
  /*Join custom data with main/core product collection. */
   $collection = $this->joinExtraTablesForCustomData($collection);
   foreach ($collection as $item)
   {
       $customProduct = $this->customProductInterfaceFactory->create();
       $customProduct->setData($item->getData());
       $customProducts[] = $customProduct;
   }
   $searchResult->setSearchCriteria($searchCriteria);
   $searchResult->setItems($customProducts);
   $searchResult->setTotalCount($collection->getSize());
   return $searchResult;
}