How to use Mongoose Populate between 2 different Schema's - express

Question

I have 2 schema's, Categories and Cards. Each Category has an array of cards, and I want to populate that array with values , but I am unsure how to go about this as the mongoose documentation is somewhat confusing to understand.
// Schemas in seperate files
// Category Schema
const mongoose = require("mongoose");
const Schema = mongoose.Schema;
const categorySchema = new Schema({
title: {
type: String,
trim: true,
max: 30,
},
cards: [{ type: Schema.Types.ObjectId, ref: "categoryCard" }],
});
module.exports = mongoose.model("category", categorySchema);
// Category Card Schema
const mongoose = require("mongoose");
const Schema = mongoose.Schema;
const categoryCardSchema = new Schema({
category: {
type: String,
trim: true,
},
name: {
type: String,
trim: true,
},
post: {
type: String,
required: true,
trim: true,
},
});
module.exports = mongoose.model("categoryCard", categoryCardSchema);
// Below is the express router file . I want users to be able to create cards for different categories , after the category is already created. It worked in postman, but it doesn't work on the front end for some reason.
router.route("/createCard").post((req, res) => {
const { title, name, post } = req.body;
newCard = new categoryCard({
category: title,
name,
post,
});
newCard.save();
category.findOne({ title }).exec((err, item) => {
if (!err) {
item.cards.push(newCard._id);
item.save();
res.send(item);
} else {
res.send(err);
}
});
});

Answer 1

You can Follow this code...
let categorys= await category.findOne({ title }).populate("cards")