Connection.prototype.transaction() return value

[kulakovAngel]

Mongoose version: 5.10.11.
Node.js version: 12.16.3.
MongoDB vresion: 4.4.3 (cloud.mongodb Atlas)

Do you want to request a feature or report a bug?
I think is a bug with Connection.prototype.transaction() return value

What is the current behavior?
This method returns a "CommandResult" instance, but not the value returned by the "fn" callback

const t = await require('mongoose')
  .connection
  .transaction(async session => {

    const newServices = await Service
      .create(services, {
        session
      });

    if (!newServices || !newServices.length) throw new Error('It\'s impossible to create new services');
    return await newVisit.save({
      session
    });
  });

console.log('transaction: ', t); // CommandResult { result: { ok: 1, ...} ... }

This example can be simplified to primitive, but the result is the same:

const t = await require('mongoose')
  .connection
  .transaction(async session => {

    await SomeModel.save({ session });
    
    return 1;
  });

console.log('transaction: ', t); // CommandResult { result: { ok: 1, ...} ... }

What is the expected behavior?
As described in the documentation, the method Connection.prototype.transaction() must return a promise that resolves to the value returned by the fn callback. In my example, for simplicity, "1" the number.

Returns:

• «Promise<Any>» promise that resolves to the returned value of fn

I expect something like the following:

const t = await require('mongoose')
  .connection
  .transaction(async session => {

    await SomeModel.save({ session });
    
    return 1;
  });

console.log('transaction: ', t); // based on the documentation it should be "1"

[vkarpov15]

Unfortunately this is a mistake in our docs. The MongoDB driver's withTransaction() function doesn't return the resolved value of the promise that the transaction() callback returns. So Mongoose can't support this unless we redo the MongoDB driver's connection handling. Sorry for the confusion 👍

[kulakovAngel]

I got it, thanks.

[meness]

@vkarpov15 It seems withTransaction() doesn't resolve the returned value. If so, please modify the return type of the helper.

withTransaction<T = void>(fn: WithTransactionCallback<T>, options?: TransactionOptions): ReturnType<typeof fn>;