brainlet/models/Category.js

const mongoose = require("mongoose");
const Post = require("./Post");
const User = require("./User");

const categorySchema = new mongoose.Schema({
    title: String,
    creator: {type: mongoose.Schema.Types.ObjectId, ref: "User"},
    posts: [Post.schema]
});

categorySchema.method("getPublicObject", function() {
    return {
        title: this.title,
        creator: this.populate("creator", User.getPulicFields()).creator,
        posts: this.posts,
        _id: this._id
    };
});

const Category = mongoose.model("Category", categorySchema);

module.exports = Category;