Use LEFT JOIN When Checking for null Attributes

[maxbucknell]

Description

It is not possible to filter an EAV collection by an attribute being null.

Fixed Issues (if relevant)

• Impossible to Filter Collection by null Attribute Value #14355: Impossible to Filter Collection by null Attribute Value

Also addresses:

• GraphQL ProductFilterInput Requires Field to be a String #14312: GraphQL ProductFilterInput Requires Field to be a String

Manual testing scenarios

As addressed by the integration test, load a product collection and try to addAttributeToFilter and select an attribute to be null. This is a correct usage of the API, and the where clause is generated correctly, as ... WHERE ((at_special_price.value IS NULL)).

However, without this diff, the join is an INNER JOIN, which automatically excludes null values.

Discussion

I have chosen to add a little complexity here, by checking for a null comparison and only then selecting a LEFT JOIN. It would work fine to use a LEFT JOIN for this all the time, but I suspect that INNER JOIN was chosen for a reason, perhaps performance. I decided it was best to respect this decision and change as little as possible.

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)

[magento-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

Hi @maxbucknell. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.3.0 release.