Model static methods: consistently allow session option?

[bathos]

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

Feature.

What is the current behavior?

Many of the static methods of Model do not allow specifying session even though they require it to behave correctly if you are inside a transaction. (The model constructor also doesn’t take an arg for this, but you can get around that by calling $session after construction.) For example:

// within withTransaction callback, assume session is ClientSession instance of transaction

const foo = new Foo;
await foo.save({ session });
console.log(await Foo.exists({ _id: foo._id }, { session })); // false — opts arg ignored

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

What is the expected behavior?

I believe all static methods that execute queries should accept the { session } option.

This isn’t a bug since it’s working as documented — exists above just doesn’t provide any way to specify the session, so it’s running the query outside the current session — but it kind of makes transactions a minefield. Many commonly used static methods do take an options object that supports session, so it’s easy to be surprised by the fact that others, even though they execute commands that take a session, don’t (seemingly at random). The resulting incorrect behavior can be hard to spot, keeping in mind that e.g., exists(query, opts) doesn’t throw, the object is just ignored, and that you might get the right result just through (bad) luck, leaving the bug hidden in waiting.

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

Node: 12.7.0
Mongoose: 5.6.9
Mongo: 4.0.11

[vkarpov15]

Thanks, will add that. We support options for most model functions, but we'll audit and make sure we support a session option for all functions where it makes sense to.

As a workaround, you can do Model.exists(query).session(session)

See Query#session() docs

[bathos]

Thanks!

As a workaround, you can do Model.exists(query).session(session)

I did discover that this worked for countDocuments() & co, but it did not seem to work for exists. It appeared that (consistent w/ the docs actually) exists does not return a query instance, but rather a generic thenable with no query methods. Is this incorrect?

Edit: I suspect because of

mongoose/lib/model.js

Line 1039 in 5c2fbc5

return query.then(doc => !!doc);

[vkarpov15]

Woops you're right, that is a mistake on my part. exists() really should return a query...