[2.3] Correct flat indexing with staging and > 500 cats

[toddbc]

Description

In a past change, entity_id was used for mapping. However, since the index stores things by entity id (not link id), this prevents it from selecting the correct row.

Additionally, there was a spurious $categoryAttributesData = []; in buildCategoryIndexData() which looks like a mistake, so the argument was ignored.

Please see magento-partners/magento2ce#65 for more detail with regard to Magento Commerce.

Manual testing scenarios

For Magento Open Source:

1. Start with a fresh DB and create 10 categories.
2. Create another 500 categories (ideally via script.)
3. Enable flat category indexing.
4. Reindex flat category.
5. Modify the name of certain categories.
6. Reindex flat category again.

Expected results:
Reindex runs successfully. All rows have correct updates.

Actual results:
Data may not update properly.

Please see magento-partners/magento2ce#65 for the Magento Commerce test scenario.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[vkublytskyi]

@toddbc These changes need to be updated as cause an integration test failure which is not part of Travis CI builds (executed by inhouse CI envirotnment):

Magento\Catalog\Model\Indexer\FlatTest::testFlatAfterCreate
Failed asserting that actual size 1 matches expected size 3.

Magento\Catalog\Model\Indexer\FlatTest::testFlatAfterMove
PHPUnit\Framework\Exception: Notice: Undefined offset: 473 in /app/code/Magento/Catalog/Model/Indexer/Category/Flat/Action/Rows.php:178.

Magento\Catalog\Model\Indexer\FlatTest::testMoveCategory
PHPUnit\Framework\Exception: Notice: Undefined offset: 471 in /app/code/Magento/Catalog/Model/Indexer/Category/Flat/Action/Rows.php:178.

[toddbc]

Thanks for catching that - updated.

Is there a way for me to run that same test, or is it supposed to work with EE linked? I must be doing something wrong - magento_integration_tests has EE stuff in it, but didn't reproduce that error through phpunit.

[vkublytskyi]

@toddbc I reproduced these test failures locally by running single integration test as described at DevDocs (CE+EE installation).

<!-- magento2ce/dev/tests/integration/phpunit.xml -->
<testsuites>
    <testsuite name="PR12345">
        <file>testsuite/Magento/Catalog/Model/Indexer/FlatTest.php</file>
    </testsuite>
</testsuites>

Your last commit fixes an the failure.