How do I reference mongoose model to another model?

Question

I have a mongoose schema for stories that looks like this:

{
    id: {
        type: Number,
        default: 0
    },
    title: {
        type: String,
        maxLength: 60
    },
    author: {
        userid: {
            type: Number
        },
        username: {
            type: String
        }
    }
    chapters: [chapter],
    numchapters: {
        type: Number,
        default: 1
    },
    favs: {
        type: Number,
        default: 0
    },
    completed: {
        type: Boolean,
        default: false
    }
}

What I'm trying to do is reference a document in a separate collection (users), and use the values of its userid and username fields in the author field. how do I do this?

current code:

storyobj.populate('author', {path: 'author', model: 'users', select: 'userid username'}, (err) => {
            if (err) {
                console.log(err)
            }
        })

---

just in case it's relevant, the structure of the users collection looks like this:

{
    username: {
        type: String,
    },
    email: {
        type: String,
    },
    password: {
        type: String,
    },
    userid: {
        type: Number
    },
    isAdmin: {
        type: Boolean,
        default: false
    },
    banned: {
        type: Boolean,
        default: false
    }
}

---

EDIT:

I've changed the author field in the Stories model to look like this:

    author: {
        type: mongoose.Schema.Types.ObjectId,
        ref: "User"
    }

This is so I tell Mongoose, "Hey, I want this field to reference a user in the User collection".

Here are some more details that I hope will be of help.

Full code:

var storydb = require('../models/stories/story');
var chapterdb = require('../models/stories/chapter');
var userdb = require('../models/user');

const file = JSON.parse(fs.readFileSync('test.json')); // this is a file with the data for the stories I am trying to insert into my database

for (const d in file) {
    var storyobj = new storydb({
        id: d,
        chapters: []
    });
    for (let e = 0; e < file[d].length; e++) {
        var abc = file[d][e];
        var updatey = {
            chaptertitle: abc.chapter,
            chapterid: parseInt(abc.recid),
            words: abc.wordcount,
            notes: abc.notes,
            genre: abc.gid.split(', '),
            summary: abc.summary,
            hidden: undefined,
            loggedinOnly: undefined,
            posted: new Date(Date.parse(abc.date)),
            bands: abc.bandnames.split(', ')
        };
        var kbv = getKeyByValue(userlookup, abc.uid);
        
        storyobj.title = abc.title;
        storyobj.numchapters = file[d].length;
        storyobj.favs = file[d][0].numfavs;
        updatey.characters = abc.charid.split(/, |,/g);
        
        storyobj.chapters.push(updatey)
    }
    storyobj.save();
}

In file, there's a unique ID representing the author of each story. kbv returns the userid associated with that unique ID (note that they're NOT the same).

Now, here's where I'm having trouble:

What I want to do is find a user matching the userid in kbv, and make that the author property in the story model.

The code I'm currently using to try and achieve that:

storydb.findOne({storyobj}, 'author').populate("author", (f) => console.log(f));

Answer 1

const Stories = require("./path/to/model");

Stories
    .find({ /* query */ }, { /* projection */ })
    .populate("author.username", ["userid", "username"])
    .then(/* handle resolve */)
    .catch(/* handle rejection */)

For this to work, you have to add a ref key to the userid key in your model, where the ref value is the name of the model it's referencing.

Story.model.js

const StorySchema = new Schema({
    author: {
        userid: { type: Schema.Types.ObjectId, ref: "users", required: true },
        /* other props */
    }
    /* other props */
});