How to filter while populating in mongoose?

Question

I want to filter results based on populated data in mongoose. How to do that?

Consider date = 2022-05-22T00:00:00.000Z

Tried code:

const attendances = await Attendance.find({ active: { $in: id } }).populate(
    {
        path: "meeting",
        model: Meeting,
        match: { date: { $lt: today } },
        select: "title date",
    }
);

Results:

  {
    _id: new ObjectId("6283fb550079acdda0cd9027"),
    meeting: {
      _id: new ObjectId("6283fb550079acdda0cd9024"),
      title: 'aaa',
      date: 2022-05-19T00:00:00.000Z
    }
  },
  { _id: new ObjectId("628579e3aa11102f928d6f1a"), meeting: null }

I want to remove the second object based on the time compared to populated data.

Answer 1

you can use aggregation to filter

const attendances = await Attendance.aggregate([
  {
    $match: {//match anything you want like normal query}
  },
  {
    $lookup : {
      from: 'meetings' //Collection's name,
      localField: 'meeting', //field you want to use to lookup
      foreignField: '_id', 
      as: 'meeting', 
    }
  },
  {
    $unwind :{
      path: '$meeting',
      preserveNullAndEmptyArrays: true,
    },
  },
  {
    $match : {
      meeting : {$ne : null} //filter meeting !== null or you can filter anything you want in meeting like bellow
      "meeting.date" : {$lt : //Date}
    }
  }
])