magento/magento2#12699: Multiselect Attribute is not saved

[andrii-dymov]

Fixed attribute loading for different entities in AbstractEntity

Description

Fixed attribute loading for different entities in AbstractEntity

Fixed Issues (if relevant)

1. magento/magento2#12699: Multiselect Attribute is not saved #12767: Multiselect Attribute is not saved for a product in the admin panel when it has a related product using another attribute set

Manual testing scenarios

Steps to reproduce

Create 2 attribute sets from the Default one.
Create a multi-select attribute and assign it to set #1.
Create a product 1 with attribute set #2.
Create a product 2 with attribute set #1 and set a product 1 as it's related product.
Save product 2 without populating the multi-select.
Edit the product 2, populate multi-select and click save.
Notice the selected option is not saved
Expected result

Multiselect Attribute should be saved for a product in the admin panel when it has a related product using another attribute set.

Actual result

Multiselect Attribute is not saved for a product in the admin panel when it has a related product using another attribute set

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.

[osrecio]

This attribute should be private

[sidolov]

Refactored according to backward compatible development requirements