What to do with a MagmaCommitError

[Chris Muller]

Thanks for the great questions.

> Now I have a Debugger with a MagmaCommitError. As you can see from the
> attachement, the User2 session still has a transaction,

The attachment shows the "transactionLevel" as 0, meaning the session
is not in a transaction.  The 'transaction' instance variable always
has a MaTransaction instance which is just a single per session to
manage the readSet (for changed-detection).  It is completely private.

so I have some
> questions:
>
> -Is this transaction invalid in some way? I've observed some possibly
> relevant protocol here (#restore? #changedObjects?)

MaTransaction is completely private.  Access with caution.

> -Supposing that it's appropiate to reapply User2 changes, do I have the
> chance to do it from the Debugger?

Magma guards its internal state, you may restart at the point your
application issued the #commit, but be sure to check the session
transactionLevel, you may need to manually send #begin to the session
first if the application code doesn't..

Likewise, if your application issued #commit: [ ... ]  and your
session is at transactionLevel 0, then of course you can just restart
from there..

> -If the Debugger isn't useful at this stage, how to apply the User2 changes?

A session that experiences a commit-conflict is no longer in a
transaction, but the local changes can still be committed.  However,
the state of the local model is now "merged" with updates from other
users.  The MagmaCommitConflictError (Exception) has a
MaFailedCommitResult, which has a collection of the objects that, in
particular, the application may wish to review, they are the ones
User2 changes now overlay the local changes.

If the application wishes to continue committing the local changes, it
may issue a #begin followed by a commit.  I must admit, it seems
unnecessary to require the application to do this..  I don't think
that would be difficult, hmm..

Or, the application may issue an #abort to cancel all local changes,
refresh all contents from the repository and start over.

 - Chris