Mongoose aggregation query fails in Jest/Mockgoose test, works elsewhere

Question

I\'m trying to create some tests for my Mongoose models, and I can\'t figure out how to get the Jest/Mockgoose test to pass for a shorthand query/aggregation pipeline (see b

Answer 1

I have faced similar kind of problem and after researching a lot I found that that it was due to older version of mongoose as earlier versions are not compatible with breaking changes in MongoDB 3.6 and above.

I upgraded mongoose version one by one and I found that it works perfectly fine with mongoose version 4.12.2 or above (mongoose@4.12.2).

You can upgrade your mongoose version by running following command:

npm install mongoose@4.12.2

Answer 2

Finally figured this out: I had to add a cursor call to the aggregation pipeline, and translate it into a stream. To maintain the Promise I had the query method return a Promise that resolves with data once the stream has ended, as below:

activitySchema.query.getUnused = function() {
    return new Promise((res, rej) => {
        let data = []
        return Activity.aggregate()
            .lookup({
                from: 'userActivity',
                localField: '_id',
                foreignField: 'activity',
                as: 'matched_docs',
            })
            .match({ matched_docs: { $eq: [] } })
            .sample(1)
            .project({ matched_docs: 0, __v: 0 })
            .cursor({})
            .exec()
            .on('data', doc => data.push(doc))
            .on('end', () => res(data))

    })
}