Roll back invalid object creations not handled by realm.write()

[elle-j]

What, How & Why?

Trying to create an invalid object (e.g. missing required properties) via realm.create() or a Realm.Object constructor would both throw and create the object (with default values for required properties), causing the object creation to not be rolled back in the following cases:

• A) During a manual transaction if the user does not explicitly catch the exception and cancel the transaction.
• B) If the user catches the exception within the callback passed to realm.write() and does not rethrow it.

This PR updates it so that the individual operation is automatically rolled back.

This closes #2638.

It also sets up somewhat related tests (currently .skiped) that can be enabled once #6355 is fixed.

☑️ ToDos

• 📝 Changelog entry
• 🚦 Tests

[elle-j]

Given that it's now 3 values, we could choose to return an object instead to clarify the return values.

[kraenhansen]

I agree, this is approaching (if its not already in) the territory that needs an object 👍

In this specific case, we might not need to pass the TableRef here at all, but we could instead pass a "rollback", "revert" or "delete" function, taking no arguments, which will call table.removeObject(obj.key).

[takameyer]

Is the TableRef really optional? Maybe i'm overlooking something, but the creator seems to always return a TableRef.

[elle-j]

..but we could instead pass a "rollback", "revert" or "delete" function, taking no arguments..

Interesting, yeah that seems more appropriate given that that's the only reason for passing the table 🙂

Is the TableRef really optional?

The creator defined on the Object class will always return the table, but for embedded objects, a custom createObj() method will be passed as part of the CreationContext. As those parts have not been modified, the table ref needed to be optional in this case.

[kraenhansen]

I just have a small suggestion 👍 But this can merge as is if you want to.

[takameyer]

Great fix!

[elle-j]

As per our team discussion, to prevent the extra oplog changes with the rollback, but still make realm.create() only throw or create an object, I'll rework the PR in tandem with #6359 and #6355.