Fix Customer custom attributes lost after save

[Thundar]

Description

The customer model has an attribute attribute_set_id that links to its attribute set. It is used while saving, as there is a check to see if its attributes are in the set or not, using this link.
We want to avoid a null attribute_set_id.

Fixed Issues

1. Saving Customer Model directly causes loss of data #12479: Saving Customer Model directly causes loss of data

Manual testing scenarios

1. Disable EAV cache.
2. Create a custom attribute for Customer entity.
3. Update a customer in the admin and add a value for this new attribute.
4. Programmatically load the customer, make some change (e.g. firstname) and then save directly using the model.
5. Reload the customer: the custom value is not lost.

No regression manual test:
6. Programmatically load the customer, add a different not-yet-defined attribute to customer (e.g. setNotYetDefined(1)) and save directly using the model.
7. Reload the customer: the custom value is still not lost, while not_yet_defined is lost.

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 @Thundar. Thank you for your contribution
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[Thundar]

Maybe related evolution: #4677
Surely related: #4694
By the comments, it should be already fixed on 2.3, but I cannot check it.

[slavvka]

Hey @Thundar. Thank you for the contribution. I have a question though. As far as I can see attribute_set_id should be pre-populated on customer instance creation (and exists during whole customer object life cycle). That gives us required variable set and a possibility to extend. I am not sure that having the code pre-population run every time you save customer is a good idea. Please consider refactoring it to pre-populate this variable in the factory, for example. Moreover the address model also may have the similar issue, that is also would be good to have fixed. And in that case the original code that you copied from updateData would be also not needed. Does it make sense?

[Thundar]

Hello @slavvka , thank you for your answer and the hints. They makes sense.
The nuisance is that the same code is both in CustomerRepository::save function and in Customer::updateData. I see that having a third replication would be worst.

The Address model benefits of a custom getAttributeSetId method (since MAGETWO-69111) that make it always not null: I added the same to the customer. This looks me the cleaner way (and it is easy to navigate). I think this is the best way to grant extendibility.
I also removed unused code.

[slavvka]

Hey @Thundar. You are right. Thank you for the contribution. Would you mind to port the PR to 2.3 as well? You could do it now or after this PR is merged with the special tool.

[magento-engcom-team]

Hi @slavvka, thank you for the review.
ENGCOM-3082 has been created to process this Pull Request

[magento-engcom-team]

Hi @Thundar. Thank you for your contribution.
We will aim to release these changes as part of 2.2.8.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.