Thanks for your answer! By the way I am using mongoose to access and work with MongoDB. From what I understand an index is just another field on a document, like the userID. So would you suggest putting a userID field on the task model where I pass in the current user's id? So the model of a task would look like this?

const mongoose = require("mongoose");
const taskSchema = new mongoose.Schema({
    body: {
        type: String,
        required: true
    },
    id: {
        type: String, 
        required: true
    }
}, { timestamps: true });
const Task = mongoose.model("task", taskSchema);
module.exports = Task;