unable to use $match operator for mongodb/mongoose

问题:

Relatively Simple Scenario:

I have this Voucher object which has a user property (of type ObjectId). I want to get the sum of all voucher values for a single user. Here is my current strategy, which returns an empty array:

Voucher.aggregate [
    { $match : { user : new ObjectId(user_id), expires : { $gt : new Date() } } }
    { $group : { _id : null, sum : { $sum : '$value' } } }
], (err, result)->

    console.log err
    console.log result

Removing the match for the user id, and leaving the expires field will return results. So the question becomes what is wrong with the match on user?

回答1:

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.

回答2:

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)}
    ]
};

回答3:

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

回答4:

use toString() method.

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