Connection.transaction: Model instance state is not reverted after a failed transaction

[juona]

Do you want to request a feature or report a bug?

Something in between, probably more of a feature since it could be a large task.

What is the current behavior?

Model instance state is not reverted after a failed transaction and trying to save it after the transaction is aborted will result in a VersionError.

If the current behavior is a bug, please provide the steps to reproduce.

This is a pseudo example, not a real-world scenario. It's enough to reproduce the problem.

const session = await mongoose.startSession();
const user = await UserModel.findById(userId).session(session);

// Simulating a failed transaction
try {
  await session.withTransaction(async () => {
    user.name = "Updated name";
    await user.save();
    throw new Error("Fail the transaction");
  });
} catch (err) {
  logger.debug("Oops, transaction failed, updating user status...");
  user.status = "NAME_UPDATE_FAILED";
  // At this point user.name has not been reverted to what it was initially.
  // Furthermore, the version index user.__v will point to a non-existent document
  await user.save(); // This fails with a VersionError
}

If after the transaction fails I reset user.name and user.__v to their initial values, the catch statement executes correctly.

What is the expected behavior?

Model instance data is reverted to what it was initially if the related transaction fails.

What are the versions of Node.js, Mongoose and MongoDB you are using? Note that "latest" is not a version.

I use mongoose 5.6.9 and for the time being I'd like to avoid the update to 5.7.12 'cause my env is quite unstable. I checked the release notes and open issues and have not noticed this behavour mentioned anywhere.

[juona]

I can appreciate the potential difficulties in dealing with this, so no easy fix expected. Perhaps a compromise solution could be implemented, e.g. automatically managing only the internal fields such as __v, etc. In case this is (for the time being?) too difficult to fix, some documentation would be nice. I could then infer from it what exact actions I have to take after my transaction fails, in order to fully and correctly reset my model instance state. Happy to hear your thoughts!

[ghost]

shouldn't you use session.abortTransaction()?

[juona]

The withTransaction helper deals with that, AFAIK. If there's an error, it aborts the transaction.