Mongo aggregation with paginated data and totals

Question

I\'ve crawled all over stack overflow, and have not found any info on how to return proper pagination data included in the resultset.

I\'m trying to aggregate some

Answer 1

A performance optimization tip:

When you use $facet stage for pagination, Try to add it as soon as it's possible.

For example: if you want to add $project or $lookup stage, add them after $facet, not before it.

it will have impressive effect in aggregation speed. because $project stage require MongoDB to explore all documents and get involve with all fields(which is not necessary).

Answer 2

If you have a lot of events, {$ push: "$$ ROOT"}, will make Mongo return an error, I have solved it with $facet (Only works with version 3.4+)

aggregate([
    { $match: options },
    {
      $facet: {
        edges: [
          { $sort: sort },
          { $skip: skip },
          { $limit: limit },
        ],
        pageInfo: [
          { $group: { _id: null, count: { $sum: 1 } } },
        ],
      },
    },
  ])

Answer 3

Did this in two steps instead of one:

// Get the totals
db.mongoAuditEvent.aggregate([{$group: {_id: "$corrId"}}, {$group: {_id: 1, total: {$sum: 1}}}]);

// Get the data
db.mongoAuditEvent.aggregate([
  {$group: {
    _id : "$corrId", 
    currentEvent: {"$last": "$event.status"}, 
    "events": { $push: "$$ROOT"}
  }},
  {$sort: {"events.timestamp": -1} }, // Latest first
  {$skip: 0 },
  {$limit: 10}
], {allowDiskUse: true}).pretty();

I would be very happy if anybody got a better solution to this though.