Mongoose: how to check if a value is in the array of a model, and append or delete it from array

Question

I'm writting mongoose in Node.js (ES6).

I have a model Channel that have an array attribute subscribers. My goal is simply to check whether an element is in this array. If yes, delete it. If not, append it.

The schema for the Channel model is like this:

import { gql } from 'apollo-server-express';

export const Channel = gql`
type Channel {
    "Name of the channel, this is the full path."
    id: ID!
    name: String!
    path: String!
    subscribers: [String]
}
`

The definition of the Channel model:

import mongoose from 'mongoose';
import {Address} from './Address.js';
export const Channel = mongoose.model('Channel',
    {   
        id: mongoose.SchemaTypes.ObjectId,
        name: String,
        path: String,
        subscribers: [String],
    });

Referring to this post, I have written the following function:

async function updateChannelSubscriber(channel_path, user_id, action){
    // 1. check whether this user_id is in subscribers of this channel
    const alreadyExistFlag = await Channel.find({
        path: channel_path,
        subscribers: { "$in" : [user_id]},
    });

    
    // 2. If yes, remove it; else, append it
    if (alreadyExistFlag === undefined){
        await Channel.findOneAndUpdate({
            path: channel_path,
        }, {
            $push : {subscribers: user_id}
        })
    } else {
        await Channel.findOneAndUpdate({
            path: channel_path,
        }, {
            $poll : {subscribers: user_id}
        })
    }
    
}

I tried calling this function by passing:

{
    channel_name: ",Books,",
    user_id: "1234",
    preference_type: ALL_MESSAGES // A enum type, not important
}

However I got this error:

 "message": "Cast to ObjectId failed for value \"1234\" at path \"subscribers\" for model \"Channel\"",

score 0 · Answer 1 · answered Feb 13 '21 at 05:35

change your approach, I didn't heard about $poll that you use in the query, is your mean $pull? but just try like this

async function updateChannelSubscriber(channel_path, user_id, action) {
  // 1. check whether this user_id is in subscribers of this channel
  const alreadyExistFlag = await Channel.findOne({ path: channel_path });
  // 2. If yes, remove it; else, append it
  if (alreadyExistFlag) {
    alreadyExistFlag.subscribers = alreadyExistFlag.subscribers.filter(
      (item) => item != user_id
    );
  } else {
    alreadyExistFlag.subscribers.push(user_id);
  }
  await alreadyExistFlag.save();
}

Mongoose: how to check if a value is in the array of a model, and append or delete it from array

1 Answers1