unable to use $match operator for mongodb/mongoose aggregation with ObjectId

Question

Relatively Simple Scenario:

I have this Voucher object which has a user property (of type ObjectId). I want to get the sum of

Answer 1

var aggregate  = [
{
                $match: {
                    'lenderId': new mongoose.Types.ObjectId(req.user),
                    '_disbursed': true
                }
            },
            {
                $unwind:'$emi'
            },
            {
                $match: {
                    'emi._settled': false,
                }
            }
];

Answer 2

use toString() method.

{ $match : { user : user_id.toString() , expires : { $gt : new Date() } } }

Answer 3

Turns out the casting of the ObjectId seemed to be the issue. It was being cast using the Schema type Object Id mongoose.Schema.Types.ObjectId when it needed to be just a pure ObjectId mongoose.Types.ObjectId.

Answer 4

When using the find method or findById the query can be only:

var query = {
    $or: [
        {'_sender':req.body._id},
        {'_recipient':req.body._id}
    ]
};

When using aggregate the query need a cast

var mongoose = require('mongoose');
var query = {
    $or: [
        {'_sender':new mongoose.Types.ObjectId(decoded._id)},
        {'_recipient':new mongoose.Types.ObjectId(decoded._id)}
    ]
};