FIX/API Always set polymorphic class name in gridfield on new records.

[GuySartorelli]

When creating a new record in a gridfield item edit form and polymorphic has_one relations have the ID set, but not the class. In polymorphic relations the ID is useless without the class.

This has caused at least one known issue (see parent issue below) where a relation is relied on for canX permissions but ultimately the relation only exists after the record has been created.

Parent issue

• Non-admin user unable to define email recipients silverstripe-userforms#1103

[michalkleiner]

I thought I submitted a PR for this in past, but could've been related to polymorphic has_one, not has_many.

Unrelated — I don't think we support two change types in the commit message such as FIX/API or ENH/DOC for automatic changelog creation, so you need to choose one or split the commit into two.

[GuySartorelli]

I don't think we support two change types in the commit message

There are two commits, one for each the API and the FIX. I don't think the PR name itself will affect the changelog.
If I'm wrong about that then let me know and I'll change the changelog tag to API as the higher priority of the two.

[michalkleiner]

True, the issue name has no role in that, forgot to check the list of actual commits. All good.

[maxime-rainville]

Can we add an explicit test for this method?

[GuySartorelli]

Sure thing

[GuySartorelli]

Test added.

[maxime-rainville]

Looks good ... I would like to see an explicit test to cover that new method.

@sabina-talipova Can you confirm that you've manually tested that this PR fixes the user form issue?

[sabina-talipova]

I've done test in my local environment. Manual tests - PASSED (NO ERROR or misbehaving), phpUnit tests in local - PASSED. Should I run other tests as well?

[GuySartorelli]

@maxime-rainville I've added the test you requested.