Mongoose pre-save hook fires, but does not persist data - node.js

Question

I am encountering a problem where my Mongoose pre.save() hook is firing, but the attribute does not get saved to the database. I have been searching for a long time without finding an answer.I found this thread, and the behaviour I am experiencing is very similiar, but OP's problem is related to the context of this, whereas I seem to have a different problem.
Here is my models.js:
'use strict';
const mongoose = require("mongoose");
const slugify = require("slugify");
let Schema = mongoose.Schema;
let BlogPostSchema = new Schema({
title: {
type: String,
required: true
},
createdAt: {type: Date, default: Date.now},
updatedAt: {type: Date, default: Date.now},
author: String,
post: {
type: String,
required: true
}
});
BlogPostSchema.pre('save', function(next) {
this.slug = slugify(this.title);
console.log(this.slug);
next();
});
// Passed to templates to generate url with slug.
BlogPostSchema.virtual("url").get(function() {
console.log(this.slug);
console.log(this.id);
return this.slug + "/" + this.id;
});
BlogPostSchema.set("toObject", {getters: true});
let BlogPost = mongoose.model("BlogPost", BlogPostSchema);
module.exports.BlogPost = BlogPost;
And here is the relevant lines in the router file index.js:
const express = require('express');
const router = express.Router();
const BlogPost = require("../models").BlogPost;
// Route for accepting new blog post
router.post("/new-blog-post", (req, res, next) => {
let blogPost = new BlogPost(req.body);
blogPost.save((err, blogPost) => {
if(err) return next(err);
res.status(201);
res.json(blogPost);
});
});
I am able to save the blog post to the database, and my console.log's correctly prints out the slug to the console. However, the this.slug in the pre-save hook does not get persisted in the database.
Can anybody see what the problem is here? Thank you so much in advance.

Answer 1

Mongoose will act according to the schema you defined.
Currently, your schema does not contain s filed named slug.
You should add a slug field to your schema.
Changing your current schema to something like this should work:
let BlogPostSchema = new Schema({
slug: String,
title: {
type: String,
required: true
},
createdAt: {type: Date, default: Date.now},
updatedAt: {type: Date, default: Date.now},
author: String,
post: {
type: String,
required: true
}
});