Configurable Product Type resource model 'getChildrenIds' method incorrect return format.

[kshaa]

Preconditions

1. Want to batch get simple product ids from configurable product ids
2. Magento version 2.4-develop

Steps to reproduce

1. Inject class \Magento\ConfigurableProduct\Model\ResourceModel\Product\Type
2. Apply array of multiple configurable id's to method getChildrenIds

Expected result

1. Returns array, matching configurable ids to arrays of simple ids
   // Start of edit
2. Expecting array to have such structure: [
   "parent id" => ["child id"]
   ]
   // End of edit

Actual result

1. Returns array [0 => [
   "child id" => "child id"
   ]]

[kshaa]

Possible solution is to replace the getChildrenIds method as such:
Original

    public function getChildrenIds($parentId, $required = true)
    {
        $select = $this->getConnection()->select()->from(
            ['l' => $this->getMainTable()],
            ['product_id', 'parent_id']
        )->join(
            ['p' => $this->getTable('catalog_product_entity')],
            'p.' . $this->getProductEntityLinkField() . ' = l.parent_id',
            []
        )->join(
            ['e' => $this->getTable('catalog_product_entity')],
            'e.entity_id = l.product_id AND e.required_options = 0',
            []
        )->where(
            'p.entity_id IN (?)',
            $parentId
        );

        $childrenIds = [0 => []];
        foreach ($this->getConnection()->fetchAll($select) as $row) {
            $childrenIds[0][$row['product_id']] = $row['product_id'];
        }

        return $childrenIds;
    }

Changed

    public function getChildrenIds($parentId, $required = true)
    {
        $select = $this->getConnection()->select()->from(
            ['l' => $this->getMainTable()],
            ['product_id', 'parent_id']
        )->join(
            ['p' => $this->getTable('catalog_product_entity')],
            'p.' . $this->getProductEntityLinkField() . ' = l.parent_id',
            []
        )->join(
            ['e' => $this->getTable('catalog_product_entity')],
            'e.entity_id = l.product_id AND e.required_options = 0',
            []
        )->where(
            'p.entity_id IN (?)',
            $parentId
        );

        $childrenIds = [];
        foreach ($this->getConnection()->fetchAll($select) as $row) {
            $childrenIds[$row['parent_id']][] = $row['product_id'];
        }

        return $childrenIds;
    }

[magento-engcom-team]

@kshaa, thank you for your report.
We've acknowledged the issue and added to our backlog.

[m2-assistant]

Hi @engcom-Echo. Thank you for working on this issue.
Looks like this issue is already verified and confirmed. But if you want to validate it one more time, please, go though the following instruction:

• 1. Add/Edit Component: XXXXX label(s) to the ticket, indicating the components it may be related to.

• 2. Verify that the issue is reproducible on 2.4-develop branch

  Details

  - Add the comment @magento give me 2.4-develop instance to deploy test instance on Magento infrastructure.
  - If the issue is reproducible on 2.4-develop branch, please, add the label Reproduced on 2.4.x.
  - If the issue is not reproducible, add your comment that issue is not reproducible and close the issue and stop verification process here!

• 3. If the issue is not relevant or is not reproducible any more, feel free to close it.

---

• Join Magento Community Engineering Slack and ask your questions in #github channel.