How to aggregate an item in an array of objects in MongoDB

Question

I don't know if someone could help me in solving this problem. I am trying to get a single item in an array of objects that matches a guarantorsId using the aggregation method in MongoDB. What I mean is, there is a users collection:-: ie

{
        "_id":1
        "loan":"0",
        "firstName":"kenneth",
        "lastName":"mac",
        "mobile":"09090000002",
        "email":"ken@gmail.com"
    }
    {
        "_id":2,
        "loan":"0",
        "firstName":"david",
        "lastName":"paul",
        "mobile":"09090000002",
        "email":"david@gmail.com"
    }
    ...more...

Then a user applies for a loan and provides two other users as guarantors. "guarantorsId" is the id of other users who needs to accept/decline to be a guarantor, while "_userId" is the person applying for the loan. ie loan collection:

{
        "_id":11aa,
        "guarantorOne":{
            "gAccepted":false,
            "guarantorsId":2
        },
        "guarantorTwo":{
            "gAccepted":false,
            "guarantorsId":9
        },
        "_userId":1,
        "amount":"5678",
        "duration":"12",
    }
    {
        "_id":"11bb",
        "guarantorOne":{
            "gAccepted":false,
            "guarantorsId":4
        },
        "guarantorTwo":{
            "gAccepted":false,
            "guarantorsId":2
        },
        "_userId":3,
        "amount":"5678",
        "duration":"12",
    }

Now, I need to find all loan request that matches a userId (ie either as guarantorOne or guarantorTwo when gAccepted is still false and also to get the _userId(the person who applied for loan(fisrtName and lastName)) from the users collection. I tried this but it didn't work;

await Loan.aggregate(
        { $match: {
                $or: [{"guarantorOne.gId": 2}, {"guarantorTwo.gId": 2}],
                $and: [{"guarantorOne.gAccepted": false}, {"guarantorTwo.gAccepted": false}]
            }   
        },{
            $lookup:
                {
                    from: "users",
                    localField: "_userId",
                    foreignField: "_id",
                    as: "user"
                }
        },{
            $unwind: "$user"
        },
        {   
            $project: {              
                "amount": 1,
                "duration": 1,   
                "user._id": 1,
                "user.firstName": 1,
                "user.lastName": 1,
                "user.middleName": 1,
            }
        }

I'm not to sure of my collection structure, if it is possible this way. Please anyone with better ideas is welcome too

Answer 1

As per your collection there is no key as guarantorOne.gId , you should use guarantorOne.guarantorsId , check below query

       await Loan.aggregate([{ $match: {
                $or: [{"guarantorOne.guarantorsId": 2}, {"guarantorTwo.guarantorsId": 2}],
                $and: [{"guarantorOne.gAccepted": false}, {"guarantorTwo.gAccepted": false}]
            }   
        },{
            $lookup:
                {
                    from: "users",
                    localField: "_userId",
                    foreignField: "_id",
                    as: "user"
                }
        },{
            $unwind: "$user"
        },
        {   
            $project: {              
                "amount": 1,
                "duration": 1,   
                "user._id": 1,
                "user.firstName": 1,
                "user.lastName": 1,
                "user.middleName": 1,
            }
        }])

Answer 2

This code below works as well

await Mainloan.aggregate([
        {
            $match: {
                $and: [
                    {
                        $or: [{"guarantorOne. guarantorsId": 2}, {"guarantorOne.gAccepted": false}],
                    },
                    {
                        $or: [{"guarantorTwo. guarantorsId": 2}, {"guarantorTwo.gAccepted": false}]
                    }
                ]
            }
        },
        { 
            $lookup:
                { 
                    from: "accounts",
                    localField: "_userId",
                    foreignField: "_id",
                    as: "user"
                }
        },
        {
            $unwind: "$user"
        },
        {   
            $project: {              
                "amount": 1,
                "duration": 1, 
                "user._id": 1,
                "user.firstName": 1,
                "user.lastName": 1,
                "user.middleName": 1,
            }
        }]);