Feature: Add forAll for cursor queries

[khaledosama999]

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

Feature Description

For cursor queries (that return the data in batches) currently there is a method forEach which is used to loop over each document returned from the query not each batch. it would be nice to loop over each batch so you can perform a bulk action on each batch.

Use Case

You want to send an email to all users currently in your system obviously you will fetch the whole user collection in batches. But it's not very efficient to send each user an email one at a time that wouldn't be very cost effective plus any mail service has a limit on the max number of bulk emails that could be sent (1000 for example). So the ideal situation would be to fetch the users in batches of 1000 and for each batch perform a bulk action of sending an email to all those users.

I can make the PR myself but I will wait for the issue approval

[vkarpov15]

I have a few issues with this. First, finding a good name: batchSize already means something else. Second, it isn't particularly difficult to do this with eachAsync:

let batch = [];
const batchSize = 1000;

await Users.find().eachAsync(async function(user) {
  batch.push(user);
  if (batch.length >= batchSize) {
    await sendEmailToUsers(batch);
    batch = [];
  }
});

[khaledosama999]

That's exactly what I did to solve it :D, but for me here's why I think it would be nice to have it as part of mongoose:

• From a functional programming point of view the function passed to eachAsync is impure since it depends on the batch array, so it could introduce all kinds of weird behavior if the user is not careful when it comes to the usage of the batch array outside of the function passed to eachAsync .

• Although the solution might seem easy I don't think it will occur to everybody especially beginners, but if mongoose has a built in function and it's mentioned in the docs that would make it a lot easier.

• And lastly this seems more readable and cleaner to me :

await Users
.find()
.batchSize(1000)
.eachBatch(async function (batch) {
await sendEmailToUsers(batch);
});

[khaledosama999]

@vkarpov15

[vkarpov15]

I think a batchSize option to eachAsync() would work if you're willing to put in a PR 👍

[khaledosama999]

@vkarpov15 Done I don't know exactly how you manage features but the feature branch was based on branch 6.0 and the PR is on branch 6.0 also I didn't want to come near the master branch as I'm assuming this is the branch used for the latest mongoose version