How to search in mongoDB if an element is in an array

Question

I'm creating the backend of my project. In this project, there are some groups, and each groups has its partecipant. I would like to make a function in nodejs that retrive all the groups that, in the partecipant field(which is an array), has a given user. Here is the schema of group:

const mongoose = require('mongoose');
const Schema = mongoose.Schema;

const GroupSchema = new Schema({
    name: {
        type: String,
        required: true,
        unique: true,
    },founder:{
        type:String,
        required: true, 
    }, partecipants:{
        type: Array,
        required:false,
    }, files: {
        type:Array,
        required: false,
    }
})

const Group = mongoose.model('Group', GroupSchema);

module.exports = Group;

For now, I wrote only this:

const getGroupByUser = (req, res) => {
    const user = req.body.user;

    Group.find()
        .then(files => res.json(files))
        .catch(err => res.status(400).json('ERROR:'+err))
}

But it obviusly returns all the groups. I don't know if there is a way to make it in the promise, or if I have to cycle throught the array, like a linear search, but for multiple cases. Any idea? Thank you

if you can give sample data and expected output in JSON

Takis
– Takis

2021-11-29 15:26:12 +00:00
Commented Nov 29, 2021 at 15:26 — Takis
– Takis, Commented Nov 29, 2021 at 15:26

Marco Bertelli · Accepted Answer · 2021-11-29 16:00:56Z

1

const getGroupByUser = (req, res) => {
    const user = req.body.user;
    const id = req.query.id;
    // if id is saved as objectId covert it using Types.ObjectId(id)

    Group.find({partecipants: id})
        .then(files => res.json(files))
        .catch(err => res.status(400).json('ERROR:'+err))
}

using {partecipants: id} you tell to mongoDb to find all group that have into the array the userId you pass in query params

answered Nov 29, 2021 at 16:00

Marco Bertelli

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