nodejs express length of list in a model as a response

Question

How can I calculate the length of a list in one of the parameters of a model, and add that length to another parameter of that same model so that it can be send back as part of the response by the api?

const mongoose = require('mongoose')
const Schema = mongoose.Schema;
const ArrayOfUser = require('../models/arrayofuser')

var usersSchema = new Schema({
    items: {type: mongoose.Schema.Types.ObjectId, ref: 'ArrayOfUser'},
    total: items.length

})
module.exports = mongoose.model('Users', usersSchema)

Answer 1

Solution

These are called virtual properties, functionality directly provided by mongoose:

Code

The way to achieve it in your case would be:

const usersSchema = new Schema({
    items: {type: mongoose.Schema.Types.ObjectId, ref: 'ArrayOfUser'},
},{
    toObject: {virtuals: true}, toJSON: {virtuals: true}
})

usersSchema.virtual('total')
    .get(function() {return this.items.length})

---

Followup to Comments:

Here is the fixed Node route method for the feedback below! Good luck :)

//GET array of users data via api
app.get('/api/v1/users', (req, res) => {
  const pagesToSkip = ~~req.query.pagesToSkip
  const pageSize = ~~req.query.pageSize
  const searchText = req.query.pagesToSkip
  // var searchText = {}
  Users.find().populate('items').exec((err, users) => {
    if (err) {return res.send(err)}
    res.send(users) // I'd recommend `res.json({users})`, but ¯\_(ツ)_/¯
  })
})

// NOTE: The `~~x` is a code-golfy way of Saying Math.floor(x)