retrieving array data in mongodb which match id

Question

Below is the schema. i want to get the answers as per matched qid, but i am getting all the answers in the answers array. i have tried almost all the queries but not able to understand why is this happening, if you could give link to other article that will be helpful too.

const id = req.params.id;
    
    Channel.findOne({answer: {qid: {$in: [id]}}})  
    .then(result => { 
        console.log(result);
        // let userAnswer;
        // userAnswer = result.answer.map(i => {
        //     return {userId: i.userId , userName: i.userId.name, answer: i.answer}
        // });
        // res.json({ans: userAnswer, question: result.content});  
    })
    .catch(err => {
        console.log(err);
    }); 





const mongoose = require('mongoose');
    const Schema = mongoose.Schema;
    
    const channelSchema = new Schema({
        name: {
            type: String,
            required: true
        },
        category: {
            type: String,
            required: true
        },
        creator: {
            type: String,
            required: true
        },
        subscribers: [{type: mongoose.Types.ObjectId, required: true, ref: 'User'}],
        content: {
            question: [{
                title: {type: String, required: true},
                userId: {type: mongoose.Types.ObjectId, required: true, ref: 'User'}
            }]
        },
        answer: [{
            answer: {type: String, required: true},
            qid: {type: mongoose.Types.ObjectId, required: true},
            userId: {type: mongoose.Types.ObjectId, required: true, ref: 'User'}
        }]
    });
    
    const model = mongoose.model('Channel', channelSchema);
    
    module.exports = model;

Does this answer your question? [Retrieve only the queried element in an object array in MongoDB collection](https://stackoverflow.com/questions/3985214/retrieve-only-the-queried-element-in-an-object-array-in-mongodb-collection) that's what you're looking for, using either `$elemMatch` or `$filter` is fine but you need to be sure input type does match with type in DB.. — whoami - fakeFaceTrueSoul, Jun 22 '20 at 18:28
what have you tried ? If you use ‘$elemMatch’ you would get only one element (first matched in array) use ‘$filter’ with projection.. — whoami - fakeFaceTrueSoul, Jun 22 '20 at 18:42
this gives me null array ```{$project:{_id: 0, answers: {$filter: {input: "$answer", as: "ans", cond: {$eq: ["$$ans.qid", id]}}}}}``` — devesh, Jun 22 '20 at 19:29
`qid` in DB is `ObjectId()`, can you print and give me input `id` ! Both types should match !! Do you mean `null array` empty array ? — whoami - fakeFaceTrueSoul, Jun 22 '20 at 20:11

score 0 · Answer 1 · answered Jun 22 '20 at 18:32

const id = req.params.id;
    
    return Channel.findOne({answer: {qid: {$in: [id]}}})  
    .then(snapshot => { 
        const results = [];
                    snapshot.forEach(doc => {
                        results.push({
                            id: doc.id,
                            data: doc.data()
                        });
                    });

                    return results;
                })
          
    })
    .catch(err => {
        console.log(err);
    });

This is the way when you are going to fetch one array record. Not tested, only to show you how to get single record from collection

retrieving array data in mongodb which match id

1 Answers1