MongoDB Aggregation - Query array of objects

Question

I have a collection with this data:

[
    {
        _id: "123",
        number: 10,
        users: [
            {
                amount: 20
            }
        ]
    },
    {
        _id: "456",
        number: 20,
        users: [
            {
                amount: 10
            }
        ]
    }
]

I need to find documents where users[0].amount is greater than or equal to number. I have the following Mongoose query:

Model.aggregate([
    {
        $match: {
            $expr: {
                $and: [
                    { $gte: ["$users.0.amount", "$number"] },
                    ...
                ]
            }
        }
    }
]);

However, this doesn't seem to be filtering the documents properly. I'm assuming $users.0.amount isn't the correct syntax. How can I fix this?

mickl · Accepted Answer · 2020-04-14 23:50:38Z

1

$expr requires Aggregation Framework's syntax so you have to use $arrayElemAt instead:

{  $gte: [ { $arrayElemAt: [  "$users.amount",  0] }, "$number" ] }

where users.amount is an array of numbers

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answered Apr 14, 2020 at 23:50

mickl

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1 Comment

APixel Visuals Over a year ago

Thanks, this works, I'll accept the answer after the timer is up

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