[1.7.0.1] Meteor.wrapAsync no longer works, returning a cursor instead of ajax results

[WayneUong]

We use Meteor.wrapAsync to access the collection aggregation up until meteor 1.6. But after upgrading to 1.7.0.1, the returned result is now a ‌AggregationCursor and no longer a aggregation result.

let rawDonations = Donations.rawCollection();
let rawAggregate = Meteor.wrapAsync(rawDonations.aggregate, rawDonations);
let res = rawAggregate(pipeline);
res => AggregationCursor

[spencern]

I think we may be seeing this in Reaction as well.

[sabativi]

I think it is a change on the mongo driver, add a .toArray at the end, this will return a promise that you can get on the client.
I may be wrong but this works for me, my app is in production with 1.7 and it is the only things that I had to do.

[WayneUong]

@sabativi Works wonderfully. But I struggle to find a way to resolve the promise. I need to get the results, and process them before returning them to clients. I know await can do that but I have to put it in an async function, which is not always possible.

[klaussner]

@sabativi is right, the new 3.x version of the MongoDB driver passes an AggregationCursor to the callback, whereas the 2.x version passed the aggregation result. From the driver changelog:

Collection.prototype.aggregate now returns a cursor if a callback is provided. It used to return the resulting documents which is the same as calling cursor.toArray() on the cursor we now pass to the callback.

The callback arguments are documented here: http://mongodb.github.io/node-mongodb-native/3.0/api/Collection.html#~aggregationCallback.

@WayneUong You can use Meteor's Promise.await in non-async functions:

import { Promise } from "meteor/promise";
// ...

// `aggregate` returns a cursor, so you don't need a callback or `wrapAsync`!
const result = Promise.await(rawDonations.aggregate(pipeline).toArray());